Senator Charles Grassley of Iowa said Trump’s comments “are not in line with my own beliefs about how the members of the military and their families should be treated.”

Senator Richard Burr of North Carolina said that “Captain Khan is an American hero in every sense of the term and the Khans deserve our sincerest gratitude.”

Said Senator Roy Blunt of Missouri: “My advice to Donald Trump has been and will continue to be to focus on jobs and national security and stop responding to every criticism whether it’s from a grieving family or Hillary Clinton.”

And Senator Marco Rubio of Florida called Trump’s comments “unfortunate” and praised Khan as a hero.

Yet as Democrats were quick to point out, most of the Republicans criticising Trump had already declared their plans to vote for him for president, and despite their collective outrage, none of them withdrew their support. Several, including House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, avoided mentioning the billionaire by name.

“No matter what Trump has said or done – from shameful personal attacks to racist outbursts – John McCain has blindly pledged to ‘support the nominee,” said Max Croes, campaign manager for McCain’s Democratic opponent, Representative Ann Kirkpatrick, in one typical response from a Democratic Senate campaign.

“McCain’s window to take a principled stand and abandon Trump has closed. There is no post-primary redemption for John McCain,” Croes added, in a reference to McCain’s August 30 primary face-off against a tea party-backed conservative.

The furore surrounds Trump’s accusations against Khizr and Ghazala Khan, whose son was killed in Iraq in 2004. Trump complained that Khizr Khan was “viciously attacking” him by appearing on stage at last week’s Democratic National Convention holding up a copy of the Constitution, questioning whether Trump had even read it and asserting the billionaire had sacrificed nothing. Trump has responded by insisting he had made sacrifices and questioning why Ghazala Khan did not speak on stage, which she later said was because she was too bereaved.

Late on Sunday, Trump supporters, including long-time adviser Roger Stone, circulated unsubstantiated accusations from an anti-Islam website about Khan. Stone tweeted a link to a post that, among other things, accuses Khizr Khan of being a “Muslim Brotherhood agent who wants to advance sharia law”.

It’s just the latest Trump-created conundrum for Republican senators who need support from Trump’s enthusiastic backers to win re-election, but risk alienating moderate Republicans, independents, minorities and women if they embrace the Republican nominee too enthusiastically.

“There’s no question that Donald Trump is making it very difficult for House and Senate candidates who are running on the ballot in November,” said Brian Walsh, a Republican strategist and former spokesman for the National Republican Senatorial Committee.

“In an ideal world we would have a candidate who would appropriately recognise his comments and apologise for them, but that’s not the situation right now.”

Candidates have also wrestled with whether to appear alongside Trump when he campaigns in their states.

When Trump appeared Monday in Columbus, Ohio, vulnerable Republican Senator Rob Portman was not on-hand; aides said he was doing previously scheduled events related to opioid legislation he has sponsored, although his schedule appeared to have him near-by. Grassley’s aides also cited scheduling conflicts as the reason Grassley did not attend Trump events in Iowa last week.

Burr, on the other hand, joined Trump on the campaign trail in Winston-Salem, North Carolina last week, and other campaigns, including Rubio’s, have said they’re open to joint appearances with Trump.

Trump is backed by all but two vulnerable Republican senators – Pat Toomey of Pennsylvania, who is still in a “wait and see” mode, and Mark Kirk of Illinois, who withdrew his endorsement after Trump’s attacks on a US judge of Mexican heritage.