Virginia Gov. Terry McAuliffe, left, greets Jeremy McPike, a Democratic candidate for Virginia’s Senate, at an Election Day rally in Manassas Park on Tuesday. (Jahi Chikwendiu/The Washington Post)

When Virginia Gov. Terry McAuliffe and his fellow Democrats study what went wrong for them in Tuesday’s crucial legislative elections, one possible mistake stands out: Their aggressive advocacy of gun control in a pivotal Senate race in the Richmond area may have backfired by producing a pro-Republican backlash.

In a race that proved decisive in enabling Republicans to retain control of the Senate, Republican Glen H. Sturtevant won the 10th District seat after benefiting from a huge turnout in conservative Powhatan County, which analysts attributed in part to the gun issue.

Sturtevant beat Democrat Daniel A. Gecker after GOP supporters ran ads blasting Gecker for trying to win the seat with $700,000 of outside help from pro-gun-control TV advertisements paid for by a group linked to former New York mayor Michael Bloomberg.

McAuliffe had backed Gecker as far back as the Democratic primary and has broken with typical past Democratic practice in Virginia by openly opposing the National Rifle Association. That approach sparked some ­second-guessing in the wake of Gecker’s loss.

“The gun thing — I would have done it differently,” Sen. J. Chapman “Chap” Petersen (D-Fairfax) said. “It’s speculation at this point, but I feel the Gecker seat was one we thought we were going to win. . . . [The gun issue] was one variable that was thrown in at the last minute.”

A Richmond Times-Dispatch editorial said Gecker “made a massive mistake” by accepting the ads from Bloomberg. “A campaign focused on guns redounded to Gecker’s despair,” it said.

Other leaders from both sides said the gun issue cut both ways because it helped energize the Democratic base in the district’s liberal neighborhoods in Richmond.

“It certainly increased the intensity for some people who were pro-Second Amendment but also for some people who were pro gun control,” said Sen. Ryan T. McDougle (R-Hanover), chairman of the Senate Republican caucus.

He and others also said that hotly contested local races, such as for sheriff and county supervisor, had boosted turnout in Powhatan.

McAuliffe stayed out of the spotlight Wednesday, and his spokesman directed questions about the election to the state Democratic organization. There, press secretary Morgan Finkelstein said it was “too early” and data were “too inconclusive” to say whether the gun issue had helped or hurt the party overall.

“I think the biggest takeaway is that we don’t have to be afraid to talk about guns,” she said.

Gecker’s loss was the key setback in an election that tarnished McAuliffe’s reputation as a political wizard, earned in multiple campaigns with his good friends and allies Bill Clinton and Hillary Rodham Clinton. He gambled big and lost in what was supposed to be his specialty: raising money and overseeing campaigns.

“It does kind of hurt his image as an effective political guy,” Del. David B. Albo (R-Fairfax) said.

In addition, McAuliffe’s failure to win Democratic control of the Senate forces him to scale back his ambitions for a legislative and governing legacy.

Virginia governors can’t be reelected, so the GOP’s continued control of both chambers of the General Assembly means McAuliffe has little to no chance of fulfilling his dreams of expanding Medicaid or passing new gun-control laws.

“It damages his legacy, certainly, as governor, because he’s not going to be able to get things he wanted,” said Jennifer Duffy, senior editor of the Cook Political Report.

Instead, McAuliffe will have to settle for having a place in history mainly as a star salesman for Virginia who cut deals to bring tens of thousands of jobs to the state, according to politicians of both parties and independent analysts.

That is an accomplishment that even Republicans welcome, but there is a caveat. Even with McAuliffe’s relentless promotion, Virginia’s current job growth under him ranks well behind that of most other states because federal budget cuts have fallen especially heavily on the state.

Virginia gained 32,000 jobs in the 12 months ending in September, a gain of 0.9 percent, according to federal data. The percentage gain was 37th among the states and the District.

Even had his party won control of the Senate, McAuliffe would have faced an effective veto in the House, where Republicans retained their large majority. But control of the Senate would have given McAuliffe more leverage.

McAuliffe can realistically hope to make progress in the next session on increasing spending for K-12 education. But that is not a heavy lift. Republicans are not averse to the idea because the economic recovery has generated enough extra revenue that a tax increase would not be necessary.

In defending his record in the campaign, McAuliffe can point to significant challenges that hampered his effort. The Democrats always face difficulty in off-year elections because their supporters are less likely to show up than Republicans.

In addition, as GOP victories in other states demonstrated, Republicans were generally more energized this year, partly because of all the attention paid to the high-profile presidential contest.

“Donald Trump probably gets some of the credit” for the Republicans’ success, said Christopher Newport University political scientist Quentin Kidd. “The primary has raised awareness. Republicans are just more tuned in right now.”

Still, McAuliffe chose to invest substantial personal political capital in the race. He raised millions of dollars, helping to make it the costliest legislative campaign in Virginia history. He brought in dozens of campaign operatives to identify potential supporters and get them to the polls and barnstormed all over the state, getting hoarse in the process.

Democrats said they welcomed the support, even if it fell short.

“All the money and people he put in helped a lot,” Senate Minority Leader Richard L. Saslaw (D-Fairfax) said. “Without him, it would have been worse.”

All that infrastructure will help McAuliffe aim for a better showing in a high-profile political context next year.

“He still has the presidential election out there, and I don’t think it’s going to hurt him in whatever he wants to do for Hillary Clinton,” Duffy said.