It’s a scenario weary Republican senators have grown accustomed to: On a given day, their 2016 presidential nominee stirs controversy, forcing them to interrupt their campaign schedules to respond. Donald Trump’s refusal on Wednesday night’s debate stage to say he would accept the results of the election presented yet another challenge to embattled incumbents focused on surviving the final three weeks of the campaign.

Many GOP Senate candidates have so far held steady against the weight of Trump. But their campaigns enter a new and difficult phase now that the final debate is in their rear view. With Clinton ahead by significant margins in the polls, Democrats have the knives out for down-ballot Republicans. And Trump, who could face further slides in the polls after this week’s debate, is running like he has nothing to lose.

On Thursday, Trump rallied his supporters with accusations of voter fraud. “I will totally accept the results of this great and historic presidential election -- if I win,” he said in Ohio. The GOP nominee went on to say that he would accept “a clear election result.”

Any effective cases Trump brought against Clinton regarding the Supreme Court, emails, and immigration were overshadowed by his doubts about the electoral process. "If you took that comment out, it might have been neutral,” said Rob Jesmer, former executive director of the National Republican Senatorial Committee. “But that probably made a bad situation worse."

Several Republican senators quickly condemned Trump’s insistence that the elections are rigged against him. “He should accept the outcome,” said New Hampshire Sen. Kelly Ayotte, who is in a neck-and-neck race in a state Clinton is leading by eight percentage points. “I don't believe there is a rigged election system.”

Arizona Sen. John McCain recalled his own concession eight years ago. "I didn’t like the outcome of the 2008 election. But I had a duty to concede, and I did so without reluctance,” he said. “Free and fair elections and the peaceful transfer of power are the pride of our country, and the envy of much of the world because they are the means to protecting our most cherished values, the right to liberty and equal justice.”

Florida Sen. Marco Rubio was among the earliest to denounce Trump’s election claims. “This election is not being rigged," he said Monday night during a debate. “We have 67 counties in this state, each of which conduct their own elections. I promise you there is not a 67-county conspiracy to rig this election.”

But Democrats are not letting Rubio or other candidates off the hook. Priorities USA, the super PAC supporting Clinton, began running ads this week tying Ayotte and Pennsylvania Sen. Pat Toomey to Trump. Campaigning for Clinton Thursday in Miami, President Obama attacked Rubio in his home state with the same ferocity he used on Trump.

"I'm even more confused by Republican politicians who still support Donald Trump," Obama said. "Marco Rubio is one of those people. How does that work? How can you call him a con artist and dangerous and object to all the controversial things he says and then say, 'But I'm still gonna vote for him?' C'mon, man!”

Republican strategists say Senate candidates are used to the terrain in which they have to consistently handle Trump, and that the debate isn’t an outlier in that regard. The RealClearPolitics polling averages shows Rubio leading Democrat Patrick Murphy by nearly five points, as Trump trails Clinton there by nearly four points.

“At this point, most voters realize that Trump is not a typical Republican and are not holding Republican candidates accountable for every utterance he makes,” said Alex Conant, who is advising Rubio’s Senate campaign. “There is an angst amongst many voters as it becomes increasingly likely that Hillary Clinton will become president, and they don't want to give her a Democratic-controlled Senate. We’re seeing a lot more ticket splitting in the polls because she is so unpopular.”

Heading into the final stretch, “The question is whether [Senate candidates] have the oxygen to make their closing argument, and I think now with the debates in the rearview mirror, I think they’ll have that opportunity,” said Josh Holmes, a Republican strategist and former chief of staff for Mitch McConnell.

Closing statements from Senate candidates include the “blank check” message that was employed successfully by Republicans around this time 20 years ago when it became clear then-nominee Bob Dole stood little chance against Bill Clinton. Republican Senate candidates this cycle have had this card in their back pockets for some time. “I think he’s headed for a pretty decisive defeat, and that happened long before he ever stopped recognizing results,” Holmes said.

Republicans may confront new challenges, though, if Trump’s numbers continue to decline. A recent Bloomberg poll showed signs of trouble for Trump among his own coalition: Clinton led by 2 points among men in a two-way contest, and by 4 points among those without a college degree.

In addition, Trump’s feud with House Speaker Paul Ryan and railings against establishment candidates could have an impact on turnout from the GOP nominee’s loyalists for other party candidates.

With a widening race, Republicans and Democrats both fear voter depression. Clinton’s lead risks weakening her message to voters to show up at the polls to defeat Trump. Republicans who stay home because they dislike both candidates would hurt Senate and congressional candidates on the same ticket.

Many Republican Senate candidates formed their own campaign ground games apart from Trump early on, so as not to be dependent on the nominee’s lagging infrastructure.

“For every sliver of Trump fans who declare they won't vote GOP down ticket because a candidate denounced Trump, there's usually an equal slice of swing voters who may warm to the Republican candidate,” said GOP pollster Robert Blizzard. “In terms of turnout, I'm less worried about Republicans staying home because of intra-party fighting, and more worried about another strong Democratic ground game that could alter the composition of the electorate to match what we saw in 2008 and 2012.”

Caitlin Huey-Burns is a national political reporter for RealClearPolitics. She can be reached at chueyburns@realclearpolitics.com. Follow her on Twitter @CHueyBurnsRCP.