The president was also reviving unproved allegations that Mrs. Clinton was part of a quid pro quo in which the Clinton Foundation received donations in exchange for her support as secretary of state for a business deal that gave Russia control over a large share of uranium production in the United States.
And he was returning to questions about Mrs. Clinton’s use of a private email server and how James B. Comey, the former F.B.I. director, handled an investigation into the matter, which was closed with no charges being filed. Mr. Trump initially cited the email case as a reason for firing Mr. Comey before conceding that it was because of the Russia inquiry.
The president’s Twitter fusillade came as he and his advisers braced for the first public action by Robert S. Mueller III, the special prosecutor named after Mr. Comey’s ouster to investigate Russian meddling in the 2016 election. As part of his inquiry, Mr. Mueller is believed to be examining whether there was collusion between Mr. Trump’s campaign and Moscow, and whether the president obstructed justice when he fired Mr. Comey.
CNN reported on Friday that a federal grand jury in Washington had approved the first charges in Mr. Mueller’s investigation, and that plans had been made for anyone charged to be taken into custody as early as Monday. CNN said the target of the charges was unclear. The New York Times has not confirmed that charges have been approved.
Multiple congressional committees have undertaken their own investigations into Russian meddling in the elections, following up on the conclusion of United States intelligence agencies that Moscow sought to sway the contest in favor of Mr. Trump — an idea that he has frequently dismissed as a hoax.
Speaking on NBC’s “Meet the Press” on Sunday, Senator Rob Portman, Republican of Ohio, said the president had been “too defensive” about Mr. Mueller’s inquiry. “We ought to instead focus on the outrage that the Russians meddled in our elections,” said Mr. Portman, who serves on the Senate Foreign Relations Committee.
Ty Cobb, the White House lawyer handling the response to the Russia investigation, said that the president’s tweets were “unrelated to the activities of the special counsel, with whom he continues to cooperate.”
The tweets came days after House Republicans announced that they were opening new investigations into two of Mr. Trump’s most frequently cited grievances: the Obama Justice Department’s investigation of Mrs. Clinton’s emails and the uranium deal.
Mr. Trump is working to fuel those inquiries. The White House acknowledged on Friday that the president had urged the Justice Department to lift a gag order on an informant in a federal investigation into Russia’s attempts to gain a foothold in the United States’ uranium industry during the Obama administration.
Critics called the move improper presidential interference in a federal criminal inquiry, but Mr. Trump’s advisers said he was merely encouraging transparency.
In recent days, Mr. Trump has suggested that he believes that the questions he has been raising about Mrs. Clinton’s conduct should put to rest any allegations about his own actions, and end the scrutiny of Russia’s meddling in the election.
“This was the Democrats coming up with an excuse for losing an election,” Mr. Trump told reporters last week. “They lost it by a lot. They didn’t know what to say, so they made up the whole Russia hoax. Now it’s turning out that the hoax has turned around, and you look at what’s happened with Russia, and you look at the uranium deal, and you look at the fake dossier. So that’s all turned around.”
Senator Susan Collins, a Maine Republican who serves on the Intelligence Committee, said on CBS’s “Face the Nation” on Sunday that while she had seen “lots of evidence that the Russians were very active in trying to influence the elections,” she had yet to encounter “any definitive evidence of collusion.”