The US President, in a series of four tweets, also said his fellow Republican “did not say anything wrong” but “could have stated his response more accurately”.
Mr Sessions told his Senate confirmation hearing he “did not have communications with the Russians” despite two conversations with ambassador Sergei Kislyak last year.
It came as George Bush’s ethics lawyer has suggested Mr Sessions should be jailed and the American Civil Liberties Union (ACLU) is calling for a perjury investigation.
“Jeff Sessions is an honest man,” wrote Mr Trump at around 9.30pm Washington DC time on Thursday.
“He did not say anything wrong. He could have stated his response more accurately, but it was clearly not intentional.
“This whole narrative is a way of saving face for Democrats losing an election that everyone thought they were supposed to win. The Democrats are overplaying their hand.
“They lost the election, and now they have lost their grip on reality. The real story is all of the illegal leaks of classified and other information. It is a total ‘witch hunt’!”
The billionaire leader of the free world has previously said leaks from his administration about ties to Russia are “real” but that the news is “fake”.
A spokesman for Mr Sessions, who was an early champion of Mr Trump during his wildcard bid for the White House, confirmed Mr Sessions had two meetings with Mr Kislyak following a Washington Post article.
But during his confirmation hearing, to replace acting Attorney General Sally Yates, the 76-year-old said: “I didn’t have, did not have communications with the Russians, and I’m unable to comment on it.”
House of Representatives Democratic Leader Nancy Pelosi has said he lied under oath and “must resign”.
Richard Painter, who was chief White House ethics lawyer under Mr Bush’s administration between 2005 and 2007, has published a stream of incendiary tweets about Mr Sessions.
“Misleading the Senate in sworn testimony about one own (sic) own contacts with the Russians is a good way to go to jail,” wrote the lawyer, who is now a professor at the University of Minnesota.
ACLU executive director Anthony Romero also said yesterday: “The American people deserve a full investigation into whether Sessions perjured himself and if he is indeed fit to serve as our nation’s highest law enforcement official.
“No one is above the law, certainly not those sworn to uphold it.”
Mr Sessions has since said he will completely step away from the FBI investigation into Russia’s links to the election.
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