Republican officials are scrambling to head off potential political trouble in Kansas, fearing that the state’s Senate seat could come into play for Democrats if Kris Kobach emerges victorious in a GOP primary on Tuesday.

Senate Republican leaders are backing Rep. Roger Marshall (R-Kan.) for the nomination, believing that he has the best chance of holding down retiring Sen. Pat Roberts's (R-Kan.) seat for the GOP.

Polling in the Senate primary has been scarce. While most Republicans believe Marshall has the advantage in the race, there are growing concerns that Kobach, the controversial former Kansas secretary of state and a staunch ally of President Trump, may eke out a win on Tuesday.

“Things have tightened considerably,” one Kansas Republican operative familiar with the race said. “I think everybody working for Marshall felt pretty good for a while, but he’s not as comfortable as he was a week ago.”

Kobach has benefited in recent weeks from a surge in outside spending aimed at boosting his primary campaign. Earlier this month, a super PAC with ties to Democrats began airing television ads in Kansas, casting Kobach as a firm ally of Trump who “won’t compromise on building the wall or getting tough on China.”

At the same time, Kobach has received help from tech billionaire Peter Thiel, who has pumped nearly $1 million into a super PAC backing the former Kansas secretary of state’s Senate bid, according to filings with the Federal Election Commission. That includes a $500,000 contribution made at the end of June.

In an effort to counter the pro-Kobach efforts, the U.S. Chamber of Commerce and a super PAC aligned with Senate Majority Leader Mitch McConnell (R-Ky.) went on the airwaves in Kansas earlier this month to boost Marshall ahead of the primary.

Democrats have largely united behind the campaign of state Sen. Barbara Bollier, a former Republican who left the party in 2018. She has repeatedly outraised both Marshall and Kobach since launching her Senate bid last year and will begin her general election with far more cash on hand than the eventual GOP nominee if she wins the Democratic nomination.

For now, Republicans have the advantage in Kansas, which hasn’t elected a Democrat to the Senate since the Great Depression. The Cook Political Report, a nonpartisan election handicapper, rates the contest as "Lean Republican."

But some Republicans fear that a win for Kobach on Tuesday would reverse their fortunes in Kansas. Kobach has often courted controversy with incendiary comments, and Republicans believe his strong stances on issues such as immigration could turn off more moderate voters.

Since launching his campaign a year ago, Kobach has yet to raise even $1 million and is heading into the primary with only about $136,000 in the bank. And what little polling there is in the Kansas Senate race shows Bollier with a narrow lead in a potential head-to-head match-up against Kobach.

Senate Republican polling reported on Thursday by The New York Times found that 30 percent of GOP primary voters would support the Democrat in the Kansas Senate race if Kobach becomes the nominee.

“Democrats haven’t won a Senate race here since when? The ’30s?” a Republican strategist familiar with the Senate races said. “Kobach is pretty much the only one who could ruin that.”

There are several factors that have contributed to the Republican hand-wringing in the Kansas Senate race, including Kobach’s loss in the state’s 2018 gubernatorial race to Democrat Laura Kelly.

Some Republicans have also become frustrated with Trump’s refusal to endorse in the primary. The president endorsed Kobach during his 2018 race.

Marshall wasn’t Senate Republican leaders’ first choice to fill Roberts’s seat. They sought for months to recruit Secretary of State Mike Pompeo to run for the seat race, though he ultimately declined to do so.

Still, Marshall has racked up a series of high-profile endorsements, including from Bob Dole, a former Kansas senator and Republican presidential nominee, and from the Chamber of Commerce, which launched a $400,000 ad campaign earlier this month to boost Marshall ahead of the primary.

Democrats need to flip three or four Republican-held Senate seats, depending on who wins the White House, to capture a majority in the chamber.

They are watching the Kansas GOP Senate primary closely, believing that the state could come into play in November and potentially add another pickup opportunity to their electoral map, which has expanded dramatically in recent months to include red states such as Georgia, Iowa and Montana in addition to longtime battlegrounds such as Arizona, Colorado, Maine and North Carolina.

“Dr. Barbara Bollier is building a strong campaign focused on the issues Kansans care about most like access to affordable health care, she’s outraising the entire Republican field combined, and she’s well-positioned to take on whoever emerges from this very nasty and expensive primary,” Stewart Boss, a spokesperson for the Democratic Senatorial Campaign Committee (DSCC), said.