Republicans are locked in a tough battle to retain control of the Senate this year, with only a four-seat majority and more than half a dozen GOP incumbents in competitive re-election races. But looming ahead is another potentially high-profile and consequential contest: a special election to replace Sen. Tim Kaine of Virginia should he and Hillary Clinton win the White House.

It’s by no means guaranteed that Kaine will need to be replaced for the final year of his term. Clinton holds a slim 2.5 percentage point lead over Donald Trump in the RealClearPolitics average, and there are two debates and five weeks for the race to shift back in Trump’s favor. But with Clinton and Kaine having led in the RCP average since the conventions this July, some Republicans are beginning to consider the potential election to replace him.

The hypothetical race would likely be a blockbuster, with no other Senate elections in 2017 and the possibility that Republicans could expand a slim majority if they retain the Senate in November or cut into Democrats’ majority if they lose control of the upper chamber.

And, if the Senate deadlocks at 50-50 with a Vice President Kaine being the tie-breaking vote – an increasingly plausible scenario given current polling in competitive races – it could give Republicans a chance to flip the majority back in their favor less than a year into a Clinton administration.

“People have clearly been giving it a fair amount of thought because it would be upon us in a hurry,” said Josh Holmes, a former chief of staff to Majority Leader Mitch McConnell and a top Republican strategist working on Senate races. “If Hillary Clinton were to win the presidency, I think that Virginia would be a really prime opportunity for Republicans to get a seat back right away. And if it’s a 50-50 Senate, obviously it’s incredibly consequential.”

If Kaine is elected to the vice presidency, Democratic Gov. Terry McAuliffe would appoint a temporary replacement, and there would be a special election in November 2017 – with another election in 2018 when Kaine’s term ends. Most Virginia Republicans who spoke with RCP predicted that Democratic Rep. Bobby Scott would be picked to replace the current incumbent, and Politico also reportedlast month that Scott is seen as the Democratic favorite.

To defeat Scott, who would be the Old Dominion’s first African-American senator and would run as an incumbent, would take a huge lift from Republicans in a shortened election season.

In RCP’s conversations with more than half a dozen Virginia and national GOP strategists, nearly a dozen possible candidates were identified, including former presidential candidate Carly Fiorina, who has lived in Virginia since running for the Senate in California in 2010; former Virginia Attorney General Ken Cuccinelli, who lost the governor’s race to McAuliffe in 2013; former Rep. Tom Davis; and several members of the state’s congressional delegation.

Few are willing to speak openly about a hypothetical race, as doing so would run afoul of  Trump by suggesting that the GOP nominee is likely to lose.

“All the Republicans have to act like they think Trump’s going to win, right?” said one longtime Virginia GOP operative. “They can’t be out saying I’m running for the Senate without saying we’re going to lose the presidential race, which is not real popular with the rank and file you’re trying to convert. People will be much more forward about this and we’ll begin to see the lay of the land better once the election is over.”

Still, the parlor games and speculation are quietly underway in the commonwealth. There are positives and negatives for each potential candidate, but because the state party decided earlier this year to hold a primary next year — if needed — rather than a convention, it opens the race to a variety of candidates. For starters, multiple Virginia Republicans said they expect some of the candidates running in the crowded primary for the 2017 gubernatorial race to switch over.

Candidates include former Republican National Committee Chairman Ed Gillespie, who nearly defeated Sen. Mark Warner in 2014; Rep. Rob Wittman; state Sen. Frank Wagner; and Corey Stewart, the chairman of the Prince William Board of County Supervisors who ran for lieutenant governor in 2013 but was defeated at the Republican convention.

Most of those candidates ruled out any chance they would change tracks and run for Senate. Phil Cox, a former executive director of the Republican Governors Association and a senior strategist for Gillespie, told RCP Gillespie is “100 percent committed to running for — and winning — the Virginia governor’s race.” He added that Gillespie has more than $1 million on hand and there are polls showing him with a wide lead in both the primary and general elections.

An aide to Wittman declined to comment about the race other than to say the candidate’s focus is on his own re-election and helping other Republicans on the ballot this year.

Wagner told RCP in an interview he is “only running for governor of Virginia. If I had wanted to go to Washington I would have done so a long time ago as a congressman.”

Stewart is chairman of Trump’s campaign in Virginia, giving him a connection with grassroots organizers and helping increase his name ID as he travels the state for the GOP nominee. He also said he’s committed to running for governor.

“Obviously I think Mr. Trump is going to win,” he said. “But obviously there’s a chance Hillary is going to win, and if that happens people are going to be looking to those candidates who have the statewide recognition, and I can understand why my name comes up but it’s just not my skill set.”

Gubernatorial candidates represent only a slice of the potential Senate contenders. Rep. Barbara Comstock is viewed as someone who could clear much of the primary field, but the one-term congresswoman is locked in a competitive re-election race this year.

Speculation about Comstock swirled earlier this year when some website domain names, including, were purchased. An aide to Comstocktold the Washington Post at the time that she was focused on her current re-election bid, and the aide didn’t respond to multiple requests for comment from RCP. One drawback for Comstock is running for the Senate would mean high-profile, competitive elections in three consecutive years.

“Everybody is waiting to see what Barbara Comstock does,” said another longtime GOP operative in the state. “The business community, assembly members, everybody is waiting to see, and obviously she has a race she’s in, so she’s not going to do anything, even contemplate this, until November.”

Comstock is viewed as someone who could bridge the gap between establishment Republicans and more conservative Tea Party types, which would be key to winning a packed primary. Several conservative candidates, including Cuccinelli and Rep. Dave Brat – the congressman who pulled off the shocking primary upset of Majority Leader Eric Cantor in 2014 – are expected to run. Cuccinelli didn’t respond to requests for comment, but Brat told RCP he would consider getting in to the race.

“It looks like the probability of this is going down. Trump’s numbers are going up,” Brat said. “If some crazy something happens, I’ll take a look at it.”

Multiple strategists also expected Fiorina to consider running, and pointed out her ability to raise money and high name ID as positives given the difficulty of a special election. She’s established some formal ties in Virginia, including former Gov. Bob McDonnell appointing her to the James Madison University Board of Visitors in 2012, but would have to answer questions about her connection to the state after having run in California just six years ago.

Frank Sadler, who managed Fiorina’s unsuccessful presidential campaign, didn’t address the hypothetical, but said, “She is focused on getting Republicans elected in 2016.” He pointed out that Fiorina has done events for Comstock, Gillespie, and Virginia congressional candidate Scott Taylor, as well as several other House challengers, Kentucky Sen. Rand Paul and multiple state parties.

If some of these possible candidates pass on the race, it could fall to Davis, who represented parts of Northern Virginia in the House for more than a decade. In an interview, he made clear there’s no vacancy yet and the goal of Virginia Republicans should be ensuring the seat doesn’t open. If it does happen, Davis said his hope would be either Wittman or Gillespie switching from the governor’s race to run for Senate, but if that doesn’t happen, he’d consider running.

“I’ve had a number of people talk to me and I’m not ruling anything out,” Davis said, “but I think it’s early at this point. I think we’ve got to put the party first.”

Another potential candidate is state Del. Jimmie Massie, who’s been barnstorming Virginia as a surrogate for Trump – something several Republican strategists said would help increase his name ID for a statewide run. Massie declined to consider the hypothetical special election in an interview, but said he’s already considered challenging Kaine in 2018.

“I am all in for Mr. Trump, I expect he is going to win on November the 8th, and I don’t think there is going to be a special election in 2017,” Massie said. “I was giving consideration long ago to running against Mr. Kaine in 2018 and that is still my position. I do not think there is going to be a race in 2017 and I am looking forward to possibly running against Mr. Kaine in 2018.”

If this hypothetical race does become a reality, it’s likely to be one of the biggest in 2017, with tens of millions of dollars flowing in on both sides. And if the Senate is split 50-50 with a Vice President Kaine holding the tiebreaker, it could represent a chance for Republicans to win back a narrow majority a year before the 2018 midterms.

For now, however, few potential candidates or other Republicans are willing to speculate about what is to come.

“It’s very hard to do much of anything right now because no one wants to be that guy that says, ‘We’re going to lose, so I’m going to do this.’ It’s all very subterranean right now,” said one longtime GOP operative. “I think there will be a quick winnowing, but it will be chaos for a couple weeks after the elections because that’s when we’ll find out for sure who’s really thinking about this.”