Updated

Democrat Christy Smith conceded the special election race for California's 25th Congressional District to Republican Mike Garcia on Wednesday, marking the first time Republicans will retake a Democratic-held congressional seat in the state since 1998 -- and, Republicans said, indicating that enthusiasm for President Trump is strong heading into the 2020 elections.

Garcia, a former Navy combat pilot, had a 12-point edge over Smith, a state assemblywoman, as of late Tuesday night in the contest for the swing-district seat vacated by Katie Hill after her resignation. Trump had declared victory on Twitter early Wednesday morning, but Smith initially held off on acknowledging defeat, as an unknown number of ballots remained uncounted.

"While it's critical that we ensure every vote is counted and recorded, we believe that the current tally shows Mike Garcia is the likely victor in the May 12 special election," Smith said in a statement posted to Facebook on Wednesday afternoon. "As such, I'd like to congratulate him."

Trump lost the district by 6 percentage points in 2016. He went out of his way to promote Garcia in recent weeks as strong on guns and immigration, and some Democrats had hoped he would be a liability in the race. Former President Barack Obama, Hillary Clinton and other high-profile Democrats all lined up behind Smith.

The seat became vacant last year after the resignation of Hill, who stepped down after admitting to an affair with a campaign worker and the House opened an ethics probe into an allegation that she was involved with a member of her congressional staff, which Hill denied.

Voters drop off ballots in a special election for California's 25th Congressional District during the coronavirus outbreak, Tuesday, May 12, 2020, in Simi Valley, Calif. Republican Mike Garcia and Democrat Christy Smith are running for the seat after the resignation of Rep. Katie Hill, D-Calif. (AP Photo/Mark J. Terrill)

Voters drop off ballots in a special election for California's 25th Congressional District during the coronavirus outbreak, Tuesday, May 12, 2020, in Simi Valley, Calif. Republican Mike Garcia and Democrat Christy Smith are running for the seat after the resignation of Rep. Katie Hill, D-Calif. (AP Photo/Mark J. Terrill)

Smith and Garcia topped a crowded field of candidates in the state’s March 3 primary and advanced to separate elections: One, on Tuesday, to fill the remainder of Hill’s two-year term, and a second in November for the full, two-year term starting in 2021.

Two years ago, Democrats picked up seven Republican House seats in California, helping the party retake control of the chamber. The GOP now holds just six of California’s 53 House seats.

The 25th District anchored in Los Angeles County, with a slice of Ventura County with the Ronald Reagan Presidential Library on its western end, has a Democratic registration edge and Hill captured the seat by 9 points in 2018.

"So proud of Navy combat vet @MikeGarcia2020 for his outstanding Election Night!" remarked New York GOP Rep. Elise Stefanik, as initial results came in on Tuedsay. "Proud to support him! I know he worked incredibly hard A LOT of swing district newly elected House Dems nervously watched these results. Big trouble for Nancy Pelosi!"

TOP REPUBLICAN ISSUES 'CALL TO ARMS,' SAYS DEMS TRYING TO STEAL 25TH DISTRICT SEAT

Added Trump: "Big Congressional win in California for Mike Garcia, taking back a seat from the Democrats. This is the first time in many years that a California Dem seat has flipped back to a Republican. Also, Tom Tiffany beat his Democrat rival BIG in Wisconsin. Two great Congressional WINS!"

Meanwhile, Trump himself put up historic numbers in the Nebraska presidential primary on Tuesday, more than doubling his 2016 total in the state. That led GOP Chairwoman Ronna McDaniel to tout what she called surging "enthusiasm" for the president's reelection.

In Wisconsin, Republican Tom Tiffany, a state senator endorsed by Trump, easily won a special congressional election Tuesday in the state's heavily conservative, rural 7th Congressional District.

Tiffany’s win over Democrat Tricia Zunker in northern Wisconsin’s 7th District comes in the state’s second election amid the coronavirus pandemic the past five weeks. Tiffany will replace former reality TV star Sean Duffy, a Republican who retired in September.

The district, which covers all or parts of 26 counties, has been vacant since Duffy’s retirement.

Trump won Wisconsin by less than a point, but carried the district by 20 points, in 2016. Trump backed Tiffany in the race, but due to the pandemic was unable to campaign in person for him.

Fox News' Andrew O'Reilly and The Associated Press contributed to this report.