Three top Republicans in Washington accused Democrats of "intimidating" William Barr in their demands that the attorney general resign amid allegations that the Department of Justice coordinated with Donald Trump to limit the sentence of former campaign aide Roger Stone.
Senate Majority Leader Mitch McConnell, Senate Judiciary chair Lindsey Graham and House Minority Leader Kevin McCarthy issued a rare joint statement from both congressional chambers to defend Mr Barr as a "man of the highest character and unquestionable integrity" after more than 2,000 former Justice Department employees and at least 10 Senate Democrats called for his resignation.
"Suggestions from outside groups that the Attorney General has fallen short of the responsibilities of his office are unfounded", the statement says. "The Attorney General has shown that he is committed without qualification to securing equal justice under law for all Americans."
Mr Trump has denied intervening in Stone's case after the president called a seven-to-nine-year sentence "a horrible and very unfair situation" and a "miscarriage of justice".
Stone was found guilty of lying to Congress and witness tampering following an investigation by Robert Mueller into Russian-backed interference in 2016 elections.
The Justice Department, headed by Mr Barr, stepped in to change those recommendations, prompting accusations that the president had intervened to protect the longtime Republican operative.
All four federal prosecutors assigned to the case subsequently stepped down.
The president then praised Mr Barr for "taking charge" of the case, though Mr Barr has suggested that Mr Trump stop discussing the Justice Department on social media, which he said made his job "impossible".
On Tuesday, the president said he agreed.
He said: "I do make his job harder. I do agree with that. I think that's true. He's a very straight shooter. We have a great Attorney General, and he's working very hard."
But the president said he should be allowed to use Twitter to discuss what is ostensibly an independent legal body because "everybody has the right to speak their mind. And I use social media. I guess I use it well, because here I am."
He also denied speaking to Mr Barr about Stone, but he said he "chose not to be involved".
"I'm allowed to be totally involved. I'm actually, I guess, the chief law enforcement officer of the country, but I've chosen not to be involved", the president said. "I could be involved if I wanted to be."
The statement from chief Republicans in Congress claimed that "the nation is fortunate that Donald Trump chose such a strong and selfless public servant to lead the Department of Justice."
"We expect that, as always, efforts to intimidate the Attorney General will fall woefully short."
More than 2,000 former Justice Department employees signed an open letter accusing the president and Mr Barr of "openly and repeatedly" engaging in political interference, "anathema to the Department's core mission and to its sacred obligation to ensure equal justice under the law" and a "grave threat" to justice, the letter says.
"Governments that use the enormous power of law enforcement to punish their enemies and reward their allies are not constitutional republics; they are autocracies."