Numerous Republican lawmakers have condemned Donald Trump’s attacks on the Muslim parents of a U.S. Army captain who died in Iraq, but none have withdrawn their support for his presidential campaign over the issue.

Their stance underlines the difficult tightrope many in the GOP have walked since Trump became their presidential nominee: They don’t support many of his comments, but still back his candidacy for the White House.

And the latest flap has given Democrats more fodder to throw at the rivals, particularly in the tight battle for control of the Senate, where Republicans hold a mere four-seat majority.

The debate began when Khizr Khan, father of Capt. Humayun Khan, a Muslim solider who died in Iraq in 2004, gave an impassioned rebuke of Trump at the Democratic convention last week. It escalated in the days that followed as Trump pushed back against Khan on Twitter, forcing GOP leaders to speak out on behalf of the Khans and their son. The back-and-forth continued Monday, with Trump repeating his accusation that Khan had “viciously attacked me from the stage of the DNC and is now all over T.V. doing the same - Nice!”

In an interview with CNN on Monday, Khan called Trump “ignorant” and “arrogant” and criticized other Republicans for not doing more to denounce their party’s nominee.

"Enough is enough,” he said. “Every decent Republican ... has rebuked this behavior, yet no one has stood up and said, ‘Enough, stop it. You will not be our candidate.’"

It was the second time since his convention speech that Khan has directly appealed to GOP leadership on Capitol Hill to push back against the nominee. Over the weekend, he singled out Senate Majority Leader Mitch McConnell and Speaker Paul Ryan on MSNBC, saying the “only reason they’re not repudiating his behavior, his threat to our democracy, our decency, our foundation, is just because of political consequences.”

After the interview, both McConnell and Ryan issued statements reiterating their opposition to a proposed ban on Muslims entering the country and praising the Khans and their son, but neither leader mentioned Trump nor backed off their support for him for president.

Republican lawmakers in difficult re-election battles fell along the same lines, offering statements rebuking Trump with varying degrees of sternness – some attacking him by name, others simply by offering support for the Khans – but not withdrawing their support for his campaign.

In perhaps the strongest criticism of Trump, Arizona Sen. John McCain, the chairman of the Armed Services Committee who is in a tight re-election battle this year, said, “I cannot emphasize enough how deeply I disagree with Mr. Trump’s statement. I hope Americans understand that the remarks do not represent the views of our Republican Party, its officers, or candidates.”

McCain invoked his own military service, in which he spent more than five years as a prisoner of war in Vietnam, as well as the service of his father and sons, in praising Khan’s sacrifice and thanking his parents for immigrating to the U.S. While he criticized Trump directly, he did not back off his support of the presidential candidate.

“I challenge the nominee to set the example for what our country can and should represent,” McCain said. “Arizona is watching. 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.”

Other Republican senators also challenged Trump directly without withdrawing their support for his candidacy, including New Hampshire Sen. Kelly Ayotte, who called Khan a “true American hero.”

“The Khan family deserves nothing less than our deepest support, respect, and gratitude, and they have every right to express themselves in any way they choose,” said Ayotte, who faces a tough re-election bid against Gov. Maggie Hassan. “I am appalled that Donald Trump would disparage them and that he had the gall to compare his own sacrifices to those of a Gold Star family.”

The flood of statements on the controversy amounted to the most forceful rebukes Republicans have made of their nominee despite numerous controversial statements the business mogul has made. Yet Democrats still seized on the issue, with nearly every Senate candidate facing a Republican incumbent issuing a statement calling on the opposition to withdraw their support for Trump.

Sen. Pat Toomey of Pennsylvania issued a statement praising the Khans and saying they “deserve our gratitude and honor. Anything else is inappropriate.” His Democratic challenger, Katie McGinty, called Toomey’s words “completely hollow.”

Ohio Sen. Rob Portman’s spokeswoman said in a statement to the Columbus Dispatch that the Republican lawmaker “does not agree with Donald Trump's remarks and believes that Capt. Khan was an American hero who gave his life for his country.” His opponent, former Democratic Gov. Ted Strickland, called the words “feeble, empty and meaningless.”

Wisconsin Sen. Ron Johnson said in a statement that Khan and others who sacrifice their lives “deserve our deepest respect and gratitude,” but did not mention Trump’s attacks.

McCain, whose rebuke of Trump was perhaps the most forceful, is facing one of the toughest re-election battles of his three-decade career in Washington. And the five-term senator was attacked from both the left and the right for his statement Monday. Democratic Rep. Ann Kirkpatrick, who is running to unseat McCain, said his refusal to back off supporting Trump proved “he no longer puts ‘country first’ and put politics ahead of standing on principle for himself or others.”

On the other hand, McCain’s conservative primary challenger, former state Sen. Kelli Ward, called the entire controversy over Khan a “cynical political stunt” and suggested McCain had fallen into a Democratic trap by criticizing the GOP nominee.

“McCain's statement today makes clear that he really wants Hillary Clinton in the White House, and his tepid ‘support’ for Trump is only disingenuous pandering,” Ward said.

Sen. Mark Kirk, the only Senate Republican up for re-election this year who has said he cannot support Trump, issued a statement saying the Khan family “should be honored--not attacked. To Mr. Trump, I would simply say hands off Gold Star families."