President Donald Trump has launched a fresh attack on Attorney General Jeff Sessions, calling him "beleaguered".
He also asked why the US justice department, which Mr Sessions leads, is not investigating Hillary Clinton.
Mr Trump has made clear he is unhappy with Mr Sessions for recusing himself from an FBI inquiry into alleged Russian meddling in the 2016 election.
Last week, the president expressed regret about appointing Mr Sessions to be the US top prosecutor.
In one of a volley of Monday morning tweets, Mr Trump said: "So why aren't the Committees and investigators, and of course our beleaguered A.G., looking into Crooked Hillarys crimes & Russia relations?"
Last Wednesday, Mr Trump told the New York Times that the former Alabama senator "should have never recused himself".
"And if he was going to recuse himself, he should have told me before he took the job and I would have picked somebody else," Mr Trump added.
During recent conversations with West Wing staff, Mr Trump has raised the possibility of replacing Mr Sessions with former New York Mayor Rudy Giuliani, Axios reports.
Mr Sessions was one of then-candidate Mr Trump's earliest supporters in Washington. He recused himself from the Russia inquiry after failing to disclose a meeting with the Russian ambassador during his confirmation hearing.
Mr Trump's online remarks come as his son-in-law, Jared Kushner, denied collusion with the Russians in prepared testimony shortly before his appearance with one of the several congressional committees that is scrutinising alleged Russian attempts to influence the US presidential election.
Mr Kushner, who keeps a very low media profile, will attend a private session on Monday before the Senate Intelligence Committee, and then appear before the House version on Tuesday.
In the statement to both congressional committees he released on Monday, he says: "I did not collude, nor know of anyone else in the campaign who colluded, with any foreign government."
"With respect to my contacts with Russia or Russian representatives during the campaign, there were hardly any," he says. At the end of the statement he speaks of "perhaps four contacts with Russian representatives" both during the campaign and after.
Mr Trump also on Monday attacked the Democratic ranking member of the House Intelligence Committee, Congressman Adam Schiff, saying: "Sleazy Adam Schiff, the totally biased Congressman looking into 'Russia,' spends all of his time on television pushing the Dem loss excuse!"
The California congressman responded to the president's tweet, writing "the problem is how often you watch TV, and that your comments and actions are beneath the dignity of the office".
The Twitter tirade, which began at around 07:00 Washington time, started with a new take on a Trump campaign motto.
"Drain the Swamp should be changed to Drain the Sewer - it's actually much worse than anyone ever thought, and it begins with the Fake News!" wrote Mr Trump, ahead of an afternoon speech on healthcare.
He added that Republicans "have a last chance to do the right thing" and repeal President Barack Obama's healthcare law.
Monday's tweets come after a weekend in which Mr Trump targeted even Republicans from his own party, saying they "do very little to protect their president".