Most congressional Republicans have stuck to a simple and — thus far — successful formula for handling Donald Trump’s frequent provocations: Denounce the comment, reaffirm support for the ticket, change the subject.    

This week, that strategy faces its sternest test.  

Trump’s pointed criticism of the parents of a slain American soldier, Khizr Khan and Ghazala Khan, who condemned Trump during last week’s Democratic National Convention, has left him falling in polls less than two weeks after he became the party’s new standard-bearer.   

It’s once again putting down-ballot Republicans in an unenviable position: Give in to mounting demands from Democrats to say they’ll no longer support Trump or be labeled a fellow critic of a war hero’s family.  

It’s not a new predicament for GOP candidates, who have castigated Trump over his proposed ban of Muslim immigrants and his criticism of a federal judge of Mexican heritage. But this controversy comes after both parties have finished their conventions and as voters begin to pay closer attention to the presidential race with less than 100 days before Election Day.   

Trump’s comments already drew an extraordinary response from Arizona Sen. John McCain, who issued a 700-word statement condemning the GOP leader’s criticism of the Khans.  

“Arizona is watching,” the longtime senator said. “It is time for Donald Trump to set the example for our country and the future of the Republican Party. While our Party has bestowed upon him the nomination, it is not accompanied by unfettered license to defame those who are the best among us.”  

He did not, however, withdraw his support from Trump. For that matter, neither has House Speaker Paul Ryan or Senate Majority Leader Mitch McConnell, both of whom were forced to issue statements Sunday criticizing Trump but stopping short of declaring that he would no longer have their support.   

Republicans are stuck in a thorny situation, caught between not wanting to alienate Trump’s loyal base of support while assuring moderate voters that they don’t agree with some of the presidential candidate’s most polarizing positions and rhetoric.  

McCain, for his part, also faces a primary challenge on August 30 against former state Sen. Kelli Ward.  

If his response was unusual, other Republican senators being challenged this year sought to issue brief rebuttals reminiscent of the kind they have offered in the past — declining to name Trump but criticizing his the sentiment he expressed.  

In a two-sentence statement, Sen. Pat Toomey of Pennsylvania said the Khans “deserve our gratitude and honor,” adding that “anything else is inappropriate.”  

A spokeswoman for Sen. Rob Portman of Ohio, meanwhile, said the senator “does not agree with [Trump’s] remarks” and reiterated his opposition to Trump’s plan to temporarily cease Muslim immigration.  

That drew a swift rebuke from Democrats, who called their Republican foes cowards for not outright disavowing their party’s leader.  

“If there is a shred of sincerity behind Portman’s statement, he would show the same kind of courage that Republican Gov. [John] Kasich has and retract his endorsement of Trump today,” said Strickland campaign spokesman David Bergstein.  

Republicans have been confident that, up until now, attempts to link Trump to candidates like Portman or New Hampshire Sen. Kelly Ayotte have been unsuccessful. Voters simply don’t believe that Trump is representative of more traditional Republicans, top GOP strategists argue, and they point to polls that show their candidates sizably over-performing the Republican nominee in battleground states.    

“Several months ago I would have bet against this strategy working, but it is working,” said Rob Jesmer, former executive director of the National Republican Senatorial Committee. “People view Trump as Trump and not as a Republican. He’s his own individual brand, but they’re willing to give those other Republicans more of a break than I think you would with a conventional top-of the-ticket nominee.”  

Democrats scoff at the GOP’s optimism, confident a barrage of TV, radio, and digital ads handcuffing Senate Republicans to Trump will whittle away the number of people willing to split their ticket between Clinton and GOP lawmakers.  

They’re also confident that controversies like this one, involving the emotionally charged subject of a parent’s dead son, will eventually break through to the public.  

It’s hard to imagine a more offensive thing to say, the Democratic Party’s presidential nominee said.  

“To launch an attack as he did on Captain Khan’s mother, a Gold Star mother, who stood there on that stage with her husband honoring the sacrifice of their son,” Clinton said Sunday during a campaign stop in Ohio. “I don’t know where the bounds are. I don’t know where the bottom is.”  

The danger for Republicans, according to one veteran GOP operative, is Trump continues to stoke the controversy.  

“This could be an issue, like the judge thing, for two weeks,” said the source, who requested anonymity to speak candidly. “And then the question becomes, do Democrats take this, which is so over the top, and use it in a commercial and mail piece to say, ‘What does it take to not support him?’”  

Contact Roarty at alexroarty@cqrollcall.com and follow him on Twitter @Alex_Roarty.

Get breaking news alerts and more from Roll Call on your iPhone or your Android.