As Donald Trump opened fire on Justin Amash, the Michigan representative who became the first Republican in Congress to call for his impeachment, Mitt Romney declined to join the fight.
The former presidential nominee and Republican senator from Utah accused Donald Trump of lacking humility, honesty and integrity - but stopped short of calling for his impeachment and removal from power.
Romney was scathing about the picture of the president that emerges from the Mueller report into Russian interference in the 2016 election, the redacted version of which he said he had spent two days reading in full. He said on Sunday its findings were "troubling, unfortunate and distressing".
But he said he did not think it was time for Congress to call for impeachment.
"I don't think there is the full element which you need to prove the obstruction of justice case," he said on CNN's State of the Union.
Such sharp but qualified criticism of Trump came a day after the Michigan congressman Justin Amash became the first Republican to break ranks and call for impeachment. In a stream of tweets on Saturday, Amash said the Mueller report showed that "President Trump engaged in specific actions and a pattern of behavior that meet the threshold for impeachment".
Amash and Romney are significant figures within their party as they stand virtually alone in having the temerity to challenge Trump in public. But the fact that Romney would not join Amash on the impeachment stage is an indication of the impenetrable wall of opposition the party is likely to erect should the Democrats initiate proceedings.
Just why became clear later on Sunday, when Trump aimed his Twitter account at Amash.
Saying he was "never a fan", he called Amash a total lightweight who opposes me and some of our great Republican ideas and policies just for the sake of getting his name out there through controversy.
Trump also accused Amash of not having read the Mueller report - the congressman made much of saying he had in fact read all 448 pages - and, while repeating familiar complaints about Mueller, wrote: "Justin is a loser who sadly plays right into our opponents [sic] hands!"
Romney, who ran unsuccessfully against Barack Obama in 2012, said impeachment was not just a legal matter. It must also, he said, "consider the practicality of politics, and the American people are just not there".
He added: "The Senate is not there either."
Despite his reluctance to go all the way into impeachment, Romney has showed himself willing to take on Trump. In April he issued a statement saying: "I am sickened at the extent and pervasiveness of dishonesty and misdirection by individuals in the highest office of the land, including the president."
He told CNN the Mueller report had distressed him.
"The number of times there were items of dishonesty, misleading the American public and media - those are not things you would want to see from the highest office in the land."
He said that in terms of three crucial features of a president - humility, honesty and integrity - "the president has distanced himself from some of the best qualities of the human character".
Such was his disgust with Trump as a presidential candidate that Romney wrote in his wife Ann on to the presidential election ballot in 2016, thereby voting for her instead. He told CNN he had not yet decided whether he would do the same when Trump is up for re-election next year.