Key swing states that may well decide the presidential race are recording some of the nation’s most erratic mail service as record numbers of Americans are relying on the U.S. Postal Service to deliver their ballots, agency data shows.

Consistent and timely delivery remains scattershot as the mail service struggles to right operations after the rollout, then suspension, of a major midsummer restructuring. In 17 postal districts representing 10 battleground states and 151 electoral votes, the average on-time delivery rate for first-class mail is 83.9 percent — 7.8 percentage points lower than in January and nearly two points below the national average. By that measure, more than 1 in 6 mailings arrive outside the agency’s one-to-three-day delivery window.

The slowdowns, which have raised alarms and suspicions among voters, postal workers and voting experts, have particular implications for states with strict voter deadlines. Michigan, Wisconsin and Georgia, for example, do not accept ballots that arrive after Election Day, regardless of the postmark. Of the states that do, there is generally a short qualifying window: In North Carolina, where polls have President Trump and Democratic nominee Joe Biden in a dead heat, postmarked ballots must arrive within three days of the election.

“There are fundamental and foundational issues with the Postal Service that go beyond voting, and there are issues with election administration that we can address,” said David Becker, executive director of the nonpartisan, nonprofit Center for Election Innovation and Research. “But the rules we have for the next 14 days are the rules we have.”

There are always variabilities in the mail, he said. “There have always been states that have firm deadlines after which no more ballots will be accepted. There has always been an element of voter responsibility along with responsibility of election officials and the Postal Service. And voters are embracing that responsibility.”

In Detroit, where Democrats are relying on heavy turnout to carry the rest of Michigan, only 70.9 percent of first-class mail was on time the week that ended Oct. 9, compared with 92.2 percent at the start of the year.

In Wisconsin — which struggled mightily with a vote-by-mail primary in August — on-time delivery fell to 84.3 percent in the Lakeland district, which encompasses most of the state. In North Carolina’s Greensboro district, which includes Raleigh and Durham, service was 10.1 percentage points lower than it had been in January. Timeliness also varied widely in postal districts in Pennsylvania and Florida.

Postal Service spokesman David Partenheimer said the agency has maintained performance standards despite surging mail volumes and challenges related to the coronavirus pandemic. The agency had made an estimated 64 million ballot deliveries — to and from election offices — through Oct. 7, agency data shows.

“The Postal Service is fully committed and actively working to handle the increase in election mail volume across the country over the next two weeks,” he said in an emailed statement to The Washington Post, adding that extra staffing and resources have been allocated to help process and deliver election mail.

Workers have been instructed to use “extraordinary measures” to accelerate the delivery of ballots, he wrote. Those measures include expedited handling, special pick-ups, and extra and Sunday deliveries.

But some postal workers say ballot-handling directives from higher-ups have been chaotic. Letter carriers in Michigan say supervisors press them to focus on package delivery toward the end of their shifts, leaving ballot collection lower on the priority list. In Pennsylvania, clerks are preparing to hand-stamp ballot envelopes in the final stretch of the 2020 campaign, to steer them away from overwhelmed processing plants.

Though government officials and election experts say municipalities have made great strides in preparing for the Nov. 3 election, mail service remains a key variable given that 198 million Americans are eligible to vote by mail. Postal leaders are scrambling to build confidence in an agency that has been maligned as a “joke” by Trump, was forced to suspend a major cost-cutting agenda and told 46 states and the District of Columbia that their election regulations were “incongruous” with mail service.

The Postal Service data reveals an agency fighting to stabilize itself before a final influx of ballots, as well as the holiday season’s onslaught of packages, greeting cards and catalogues.

“In the current state of the world, there is nothing a voter could do to work around problems in the post office,” said J. Remy Green, an attorney who represents a group of voters in a lawsuit against the Postal Service in federal court in the Southern District of New York.

“I think at the end of the day, the damage that has been done here, it’s not just service performance and quantifiable damage,” Green said. “It is a kind of psychic damage to the confidence of voters and confidence in the vote.”

According to a Washington Post-University of Maryland poll conducted by Ipsos in late August, 34 percent of registered voters said they were not confident their vote would be counted correctly if submitted by mail. And 37 percent were only “somewhat” confident. More than 60 percent of respondents said they had never before voted by mail.

A representative from the Trump campaign declined to comment. The Biden campaign did not immediately respond to a request for comment.

The Postal Service began the year moving 91.8 percent of all first-class mail on time — below its internal goal of 95 percent but within the realm of reliable service. The national rate hovered in the low 90s until mid-July, roughly a month into the tenure of Postmaster General Louis DeJoy, a former supply-chain logistics executive and major Trump financier who implemented a stricter transportation schedule that banned late and extra deliveries, and other cost-cutting measures.

Meanwhile, regional vice presidents and local managers were instructed to cut hours among a 630,000-member workforce already flattened by the pandemic. The Postal Service also mothballed nearly 700 high-speed mail-sorting machines and removed more than 1,500 public collection boxes, moves the agency says were planned before DeJoy’s arrival.

The postmaster general suspended those moves in August after public and congressional pushback, but he declined to replace machines already disconnected (many had been trashed or scrapped for parts) or replace the collection boxes. The Postal Service maintains it has ample capacity to process election mail.

But postal workers say those changes have made their jobs more difficult and contributed to the delays. Mail is no longer sorted locally — instead items are sent to centralized processing facilities that cover larger geographic areas — making late and extra trips crucial components of timely delivery. Fewer sorting machines means more mail is hand-sorted, which is time-intensive and has a greater margin of error. It also means mail can sit around longer before processing.

Still, on-time service has improved since early August, after DeJoy suspended his changes and after seven federal courts intervened on behalf of 19 states and voters groups. Judges in New York, Pennsylvania, Washington state and D.C. ordered the Postal Service to authorize late and extra trips to deliver election mail, including ballots, ballot applications and voting information.

The Postal Service, though, continues to struggle with issues that are independent of but were exacerbated by DeJoy’s policies, according to postal workers and logistics experts.

The front lines remain understaffed and rely heavily on overtime hours to accomplish basic tasks. During the summer, employees routinely worked 60 hours or more per week, say workers and organized-labor leaders. Now, as the holidays approach and the Postal Service grapples with surging package volumes, overtime hours have soared.

The agency recorded 3.3 million overtime hours, or 21.1 percent of all work hours, during the week of Oct. 15, according to documents filed in the Pennsylvania lawsuit. Overtime hours typically make up 10 to 13 percent of all hours within a two-week pay period.

Though election mail and packages are processed on separate machines, they still funnel out to individual carriers for delivery, leaving the agency to decide which has priority.

The Postal Service has a vested interest in both. Ballots are profitable because municipalities cover the cost if they are mailed without postage, while packages are a core and growing part of the service’s finances.

Postal workers say that tension is clear in Michigan, especially in Detroit’s suburbs. Letter carriers say they receive messages daily telling them to prioritize packages — which often have guaranteed delivery windows — over other items, including election mail. Carriers have taken to sorting through their satchels mid-route to pull out ballots and pieces of voting information so they can prioritize them on their own, according to two letter carriers who spoke on the condition of anonymity to avoid retribution.

The frequency of mail delivery also varies widely by Zip code, even on postal routes within minutes of one another. In facilities that serve Detroit’s mostly White suburbs, staffing has remained steady, the workers said, and residents can expect delivery daily. If a piece of mail is late, they said, it will probably arrive the next day.

But in more racially diverse neighborhoods, they said, mail delivery typically occurs twice or three times a week unless a parcel is in the mix.

“I walked around a little bit — it was a mess in there,” one of the letter carriers said of a post office that serves Detroit. “There was mail everywhere. And not mail everywhere in the sense that carriers come in the morning and 'This is my route for the day. I’ve got to [sort] this up and get out of here.’ This was mail everywhere because no one is there to carry that mail.”

The Detroit postal district extends 130 miles north and 110 miles west, covering about a quarter of the state and including communities with predominantly Black populations. It also had the worst mail service in the country the week that ended Oct. 9. Meanwhile, the Greater Michigan district — which covers the rest of the state, and rural areas that helped deliver the state to Trump in 2016 — was in line with the national average, and 16 percentage points better than Detroit.

Simple awareness of the delivery issues is one of the best ways to protect mailed ballots, said Christopher Thomas, a fellow at the Bipartisan Policy Center think tank who was Michigan’s longtime director of elections.

“There might be a little faith in the postal system in the sense of the pressure being on right now for them to handle election mail,” Thomas said. “It’s distinctive mail for them to see and pull out. And people who live in those areas know that their mail is not dependable. The hope is that they know not to test that out.”

Most of Wisconsin is contained in the Lakeland postal district, where mail service is 6 percentage points below January levels. Voters have requested 1.4 million ballots, nearly half of the 3 million that state residents are projected to cast. They have already returned 61.4 percent of those ballots, a rate that dwarfs the national average of 22.7 percent, according to the United States Elections Project.

Mail service in pockets of Florida and Pennsylvania also could prove decisive.

Without Florida and its 29 electoral votes, Trump’s path to 270 electors is exceedingly difficult. In the heavily Democratic South Florida district, mail service is the worst in the state, at 82.8 percent. In the Gulf Atlantic district, which includes the northern cities of Jacksonville, Tallahassee and Pensacola, delivery stands at 83.4 percent. The Suncoast district, which includes Orlando, features some of the most heavily conservative areas in the state. Its delivery rate is 88.1 percent, down from 90.9 percent at the start of the year.

The unpredictable mail service, coupled with Florida’s firm election-night cutoff for ballot delivery, has labor leaders worried.

“Everything has been running differently between the three districts. There’s no consistency,” said Al Friedman, president of the Florida State Association of Letter Carriers. “You knew this election was coming four years ago. You knew the amount of political mail was going to be the worst. You predicted this in May — the worst year for political mail ever. And you didn’t plan.”

Mail service in Pennsylvania similarly varies by region, with better and more consistent results recorded in areas that are primarily rural, suburban and conservative.

The Western Pennsylvania district, which encompasses Pittsburgh and its suburbs and exurbs, traditionally has some of the best on-time rates in the country. The on-time rate of 89.4 percent exceeds the national average. The Central Pennsylvania district, a Republican stronghold, has an 83.2 percent on-time rate.

But the Philadelphia Metro district, which Democrats need to dominate to offset GOP votes in the rest of the state, is one of only six districts in the country with on-time service below 80 percent. Staffing shortfalls remain a chronic issue, according to postal employees in the state. In Philadelphia, workers are preparing to cull ballots, process them by hand and deliver them to local election officials to avoid having to send them to regional processing plants, where the sorting system moves slower.

“It’s hard to tell a voter with certainty,” said David Thornburgh, president of the local good-government group Committee of Seventy, “how long it will take the post office to deliver their ballot.”