Democratic candidates running for Congress this year collectively raised more than $1 billion for their campaigns — a record-shattering sum that highlights the party’s zeal to retake the House and Senate and underscores the enormous amount of money flowing into the midterm races.

The $1.06 billion raised through the end of September surpasses the nearly $900 million collected by Republican candidates for Congress in 2012 — previously the largest haul registered by a single party by this point in the election cycle, according to a Washington Post analysis of Federal Election Commission records.

And it is the first time since 2008 — when Democrats swept the White House and both chambers of Congress — that Democratic candidates for House and Senate have outraised Republicans in direct contributions to candidates’ committees.

Republican candidates for Congress raised $709 million through September, FEC records show.

While the fundraising shows remarkable strength on the part of Democrats, it remains to be seen whether the financial advantage can translate to electoral success, said Brendan Glavin, researcher at the nonpartisan Campaign Finance Institute, which analyzes historical campaign finance records.

“Money provided the platform and provided the ability to get out in front of the voter,” he said. “We’ll see what happens in the final step.”

The figures do not include candidates who are no longer on the ballot or fundraising by outside groups that raise and spend unlimited amounts to support or oppose candidates. Candidates will continue to raise money until, and beyond, the Nov. 6 election.

Sheila Krumholz, executive director of the Center for Responsive Politics, said in a statement Wednesday that this year’s midterm election is on track to becoming the costliest congressional election cycle in U.S. history.

“We expected to see the numbers climb, as they typically do, but the astonishing spike in campaign donations is a solid indicator of the intensity driving this year’s campaigns,” she said.

Democrats are also raising more money than Republicans in donations of less than $200 typically viewed as a sign of grass-roots support. Democrats on the November ballot raised $205 million in such donations — more than three times the amount Republican campaigns pulled in, The Post’s analysis shows.

ActBlue, a fundraising platform for Democratic candidates and causes, has been key to the infusion of cash coming in smaller, recurring amounts this year. ActBlue allows donors to give on their smartphones, with the money transferred to the campaign committee the next day.

In the third quarter alone, Democratic candidates and liberal organizations raised more than $385 million from 8.2 million unique contributions through ActBlue, which is more than the amount of money donors gave through the platform in the entire 2014 midterms, the group said.

Since 2017, 4.6 million people have donated through ActBlue, and 60 percent of those donors were first-time contributors, most of whom then went on to give repeatedly, said Erin Hill, executive director of ActBlue. She said giving to political campaigns has become a way for people to express their displeasure over President Trump.

“We’re in this time of historic civic engagement,” Hill said. “People are marching and taking all sorts of action — protesting, calling their representatives and making small-dollar donations.”

Some of those who amassed the most were self-funded, meaning they gave a large amount of money to their own campaign.

The two Democratic candidates for Senate who have raised the most money so far this election are Rep. Beto O’Rourke, who raised a record-setting $61.7 million in his quest to unseat Texas incumbent GOP Sen. Ted Cruz, and Missouri Sen. Claire McCaskill, who raised $28.6 million.

The two GOP Senate candidates who have amassed the most money are Gov. Rick Scott (Fla.) and Robert Hugin (N.J.), who are both largely self-funding their campaigns.

On the House side, the candidates who have amassed the largest war chests so far are Democrat David Trone, in Maryland’s 6th Congressional District — who gave himself most of the $16.5 million he raised — and Rep. Devin Nunes (R-Calif.), chairman of the House intelligence committee, who has raised $10.6 million so far for his reelection.

Democratic candidates who survived tough primary battles have received an infusion of cash in the third quarter as they stocked up for their general election fight.

This was especially the case in the most competitive House seats, where first-time challengers raised $3 million or more from July through September.

It is unusual for first-time House candidates to raise $3 million or more in one quarter, Glavin said. House candidates who raise such sums tend to be in House leadership, incumbents who are prolific in raising large amounts of money through mail solicitations, and those who self-funded their campaigns, according to a CFI analysis.

Yet in the third quarter of 2018 alone, several Democratic challengers in the most competitive House races posted remarkable hauls. Among them were $4.4 million from Scott Wallace in Pennsylvania’s 1st Congressional District, $3.8 million by Katie Hill in California’s 25th District, $3.8 million by Antonio Delgado in New York’s 19th District and $3.7 million by Amy McGrath in Kentucky’s 6th District.

The FEC data analyzed by The Post for this story included fundraising figures from some Democratic challengers to Democratic incumbents, mainly in a handful of congressional races in California and Louisiana. The Post’s analysis focused on candidate committees’ fundraising data as of Sept. 30 for those running for the House and Senate in the Nov. 6 general election.