Senior Senate Republicans are privately warning the White House to take Attorney General William Barr’s frustrations with President Trump seriously, saying it would be a grave mistake to allow the top Justice Department official to resign.

Congressional Republicans, big fans of Barr’s efforts to reform Justice Department practices and examine the origins of the Russia investigation, are not concerned that Trump might fire Barr. But they take seriously the prospect the attorney general might quit. Knowledgeable GOP insiders say that Barr’s interview with ABC News, in which he said Trump’s tweets on Justice Department matters make it “impossible” for him to do his job, was not bluster.