They’ve backed him through scandal after scandal. But concerns over Ukraine, Syria and the G7 summit are proving too much for some

No call summary has yet emerged of a phone chat Donald Trump held with Republican members of Congress on a retreat at Camp David last Saturday.

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But hours after the call, the president announced that he had done a most un-Trump thing: reversed a decision to host next year’s G7 summit at one of his own properties, “based on both Media & Democrat Crazed and Irrational Hostility”.

The real reason Trump backed down on the G7 decision, according to associates from his own party, was that moderate Republicans warned him he had gone too far, and that the effort of defending him was becoming too much – even for them.

“He had no choice,” the former New Jersey governor Chris Christie said on ABC’s Sunday program This Week. “It shouldn’t have been done in the first place. And it’s a good move to get out of it and get that out of the papers and off the news.”

The moderate Republicans who might waver on Trump – who might lose their seats in the next election if their positions on Trump diverge too far from their constituents – are for now concentrated in the House of Representatives, which is led by Democrats and where Trump could be impeached later this year.

But Trump’s removal from office would require a much larger Republican defection, requiring about 20 Republican senators to vote to convict Trump in a Senate trial following potential House impeachment.

The notion that most Republicans have a breaking point when it comes to Trump mostly went out the window during the 2016 campaign, when Trump was caught on tape bragging about sexual assault, and in the first two years of his presidency, which have witnessed a growing humanitarian crisis on the southern US border, a trade war hurting US farmers and an unprecedented attack on judicial and constitutional norms.

Through it all, Republicans have held fast.

But the situation in Washington is now extremely fluid, and recent events have gone heavily against the president.

With impeachment looming, Trump’s poll numbers foundering, video circulating of Kurds stoning retreating American troops in Syria, critical op-eds piling up and Congress preparing to receive testimony this week from what could be some of the most damaging witnesses for Trump yet, the Republican wall protecting the president is showing more and more hairline cracks.

[Republicans] are horrified that the White House chief of staff admitted it was a quid pro quo Michael Bennet

Congressional committees holding the impeachment inquiry were scheduled on Tuesday to take testimony from Bill Taylor, the former head-of-embassy in Ukraine and a career diplomat whose text message exchanges with other diplomats, revealed earlier this month, included the memorable line: “As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign.”

Later in the week, Congress is scheduled to hear from witnesses from the defense department and the National Security Council. In a tweet on Monday, two witnesses from the Office of Management and Budget, which was involved in withholding military aid to Ukraine, announced they would not appear before Congress.

“I saw some Fake News over the weekend to correct,” tweeted Russ Vought, the acting director of the office and one of the witnesses to be called. “As the [White House] letter made clear two weeks ago, OMB officials – myself and Mike Duffey – will not be complying with deposition requests this week. #shamprocess.”

But Vought’s tough talk attacking Democrats was mostly unheard outside of the innermost White House circles.

The Senate majority leader, Mitch McConnell, published an op-ed in the Washington Post criticizing Trump’s Syria policy; Senator Mitt Romney diagnosed “an inflection point in American history”; even Senator Lindsey Graham, one of Trump’s most stalwart defenders, claimed to be persuadable on impeachment.

Asked whether he was open to the possibility that Trump had committed wrongdoing in pressuring Ukraine to investigate Joe Biden, Graham told Axios’s Jonathan Swan: “Sure. I mean ... show me something that ... is a crime.”

The gestures of dissent added to a growing outrage over Trump’s leadership in the US military, signposted last week by a New York Times op-ed titled Our Republic Is Under Attack From the President, by Adm William McRaven, who commanded the mission that killed Osama bin Laden.

Trump’s decision to send the tax dollars tied to hosting the G7 summit to one of his own properties, announced by the acting White House chief of staff, Mick Mulvaney, last Thursday, led many rank-and-file members of Congress to find their voices, from Representative Francis Rooney of Florida (“I’m still thinking about it, you know?”) to Representative Mike Simpson of Idaho (“I have no doubt that Doral is a really good place – I’ve been there, I know. But it is politically insensitive”) to others who spoke with the Washington Post.

Facebook Twitter Pinterest Senator Lindsey Graham suggested he was open to the possibility that Trump had committed wrongdoing over Ukraine. Photograph: Saul Loeb/AFP via Getty Images

Donald Trump Jr, the president’s son, indicated that the White House was carefully watching which Republicans get out of line. Trump Jr retweeted a list of 23 House Republicans who were slow to sign on to a move to censure Adam Schiff, the House Democrat leading the impeachment inquiry.

Trump Jr’s enemies list might be about to grow. The Democratic senator Michael Bennet told CNN that his Republican colleagues were “horrified by the president’s behavior and they’re horrified that he invited Ukraine to interfere in our elections, they’re horrified that the White House chief of staff admitted it was a quid pro quo”.

After admitting it, Mulvaney attempted to deny a quid pro quo between Trump and Ukraine. But that argument strained credulity even inside Fox News, the erstwhile base for unquestioning Trump support.

Trump has a built-in firewall in Fox News. According to a PRRI poll released Monday, 98% of Republicans who watch Fox oppose removing Trump, and 71% of them “strongly” approve of Trump. That contrasts with 39% of Republicans who say they do not watch Fox regularly but strongly approve of the president.

Before he reversed his G7 summit decision, Trump would have seen multiple Fox News personalities questioning the political wisdom of the move. They echoed the Fox host Neil Cavuto, an occasional critic of the president who had offered an unusually bareknuckle question to a Trump supporter earlier in the week.

Doesn’t it “look bad”, Cavuto asked the Trump apologist, Greg Jarrett, that Trump pressed Ukraine to investigate Biden?

“It looks bad to Democrats,” Jarrett said. “It does not look bad to me.”

Cavuto was led to publicly wonder about a point that could apply to many Republicans: “Do you fault the president for anything?”