In this photo, 25th District congressional candidate and former Navy combat pilot Mike Garcia addresses supporters in January in Simi Valley, California.
Washington CNN  — 

The race to see who will fill the House seat left vacant when former Democratic Rep. Katie Hill resigned last year amid controversy will soon be decided with a special election taking place Tuesday.

The congressional district – California’s 25th, which encompasses parts of Los Angeles and Ventura counties and spans suburban and rural areas – is being fiercely contested.

Democrat Christy Smith, a state assembly member, faces off against Republican Mike Garcia, a businessman and Navy veteran who has never before held political office.

The special election will decide who serves out the remainder of what would have been Hill’s first term in office. But whatever the outcome, there will be a rematch. That’s because Smith and Garcia are also running as candidates for a November general election that will determine who holds the seat in the next session of Congress.

The seat went from red to blue when Hill won in 2018. Democrats want to keep the seat, but the party faces more challenging terrain now that Hill no longer holds the seat with an incumbent advantage. Republicans, meanwhile, are hoping to win back what they lost by flipping it back to red.

California Assemblywoman Christy Smith, a Democrat from Santa Clarita, speaks in a June 2019 session of the California Assembly in Sacramento.

In a sign of how competitive the race has become, the non-partisan Cook Political Report moved the race from “lean Democratic” to “toss up” in April.

Losing the seat would be a blow to Democrats, and Republicans would be sure to seize on any victory as they fight to try to win back the House majority in the fall.

One Democratic strategist told CNN that national Democrats have long viewed the seat as more difficult to win during a stand-alone special election than during a November election either for a congressional midterm or with a presidential candidate on the ballot, in part because they would expect higher Democratic voter turnout when other high-profile races were taking place at the same time.

“It’s a red seat in a special election, a purple seat during a presidential primary and it trends more blue in a November election, especially with a presidential candidate at the top of the ticket,” the strategist said.

Once a rising star in the Democratic Party, Hill announced last year that she would resign from Congress amid an ethics probe into allegations that she engaged in an improper relationship with a congressional staffer. Hill denied having a relationship with her congressional staffer, but did admit to a relationship with a campaign staffer before taking office.

Another factor adding uncertainty to the race is the fact that it is taking place during the coronavirus pandemic.

Voting amid the pandemic has become a flashpoint with President Donald Trump, who has endorsed Garcia, weighing in to claim without evidence that the election is “rigged.” Trump has further claimed that a voting booth system was installed “in a highly Democrat area,” despite the fact that the election was “supposed to be mail in ballots only.”

It’s not true, however, that the special election was intended to take place exclusively with mail-in ballots.

In March, California’s Democratic Gov. Gavin Newsom issued an executive order requiring vote-by-mail ballots to be sent to every registered voter in the district. But the order also “authorized and encouraged” election officials to make in-person voting opportunities available. There will be limited opportunities for in-person voting with multiple locations accessible to voters starting on May 2 through election day.

Los Angeles County election officials recently announced that a vote center would open up in Lancaster, California. Nearly a quarter of Lancaster voters are black, and Democrats argued that the absence of polling locations in that part of the district disenfranchised voters of color.

But Democrats weren’t the only ones calling for a vote center in the area. A press release from the Los Angeles County Registrar-Recorder and County Clerk announcing the news specifically said that the request to add the center came from the Lancaster mayor, who is a Republican elected official.

California Secretary of State Alex Padilla, a Democrat, said in a statement, “Trump’s lie filled Twitter tantrum is a dangerous preview of the General Election, where he will seek to delegitimize any election results he does not like. Expanding vote-by-mail and providing ample in-person voting locations during a pandemic isn’t a partisan issue – it’s the right thing to do to protect voting rights and public health.”

Garcia tweeted on Saturday that Smith and her Democratic allies “are desperate and trying to change the rules to steal an election,” adding, “We can’t let them succeed!!”

“Mike Garcia has made it clear from the start that he is in lockstep with Donald Trump and will put Trump’s needs before the district, leaving CA-25 residents to ‘fend for themselves,’” Kunal Atit, Smith’s deputy campaign manager, said in a statement.

“Now he is working with the President to weave baseless conspiracy theories to disenfranchise African American and Latino voters and cast doubt on the integrity of our election. This behavior shows just how out of touch he is with our values,” he added.

Lance Trover, a spokesman for the Garcia campaign, said in a statement, “The differences between Mike Garcia and Christy Smith couldn’t be more clear - Mike is a former Navy fighter pilot and small businessman who wants to lower taxes, while liberal Assemblywoman Smith hasn’t met a tax she didn’t want to raise on Californians.”

The Garcia campaign has promised that the Republican candidate would “defeat socialism,” work to “build the wall,” and “enact term limits to get rid of career politicians.”

In his endorsement of Garcia, Trump has said that he “Loves our Military, and Vets,” is “Strong on Crime, the Border, and Second Amendment” and “has my Complete and Total Endorsement!”

The Smith campaign, meanwhile, has sought to closely tie Garcia to the President while condemning Trump’s response to the coronavirus pandemic.

Smith has been endorsed by a number of high-profile Democrats, including former President Barack Obama, former Democratic presidential nominee Hillary Clinton, House Speaker Nancy Pelosi and more.

CNN’s Abby Phillip contributed to this report.