Top Republicans are urging Attorney General Jeff Sessions to remove himself from an FBI probe into alleged Russian interference in the US election.
He is under fire after it emerged he met Russia's envoy during the election - despite claiming he had had "no communications with the Russians".
Mr Sessions, who called the accusations against him "unbelievable" and "false", is holding a news conference soon.
President Donald Trump said he has "total" confidence in Mr Sessions.
Speaking on a trip to an aircraft carrier in Virginia, he said he "wasn't aware" Mr Sessions had held two meetings last year with the Russian envoy to the US.
Asked if he thought America's top prosecutor should recuse himself from the FBI investigation, he replied: "I don't think so."
"I think he probably did," Mr Trump added when asked if his attorney general had testified truthfully at his confirmation hearing.
But Democratic politicians say Mr Sessions misled the committee and should resign.
Democratic members of the House Judiciary Committee have asked the FBI to launch a criminal investigation into whether Mr Sessions lied to Congress and committed perjury.
Claims of Russian interference in the election have dogged President Trump.
The US intelligence community believes the alleged Russian hacking of Democratic organisations was carried out to help Mr Trump defeat Democrat Hillary Clinton.
Mr Trump's National Security Adviser, Michael Flynn, was fired last month after he misled the White House about his conversations with Russian ambassador Sergei Kislyak, allegedly regarding sanctions against Moscow.
What is Mr Sessions accused of?
During his confirmation hearing on 10 January, Mr Sessions was asked: "If there is any evidence that anyone affiliated with the Trump campaign communicated with the Russian government, in the course of this campaign, what will you do?"
Mr Sessions responded: "I'm not aware of any of those activities. I have been called a surrogate at a time or two in that campaign and I did not have communications with the Russians. And I'm unable to comment on it."
However, it has now emerged that Mr Sessions and Mr Kislyak held a private conversation in Mr Sessions's office in September and had spoken earlier in the summer at a meeting with several other ambassadors.
Mr Sessions had meetings with more than 25 foreign ambassadors in the course of the year.
But his meetings with Mr Kislyak came while he played a prominent part of Mr Trump's campaign team - the so-called surrogate - and amid growing reports of Russian meddling in the US election.
Did Mr Sessions mislead the hearing?
His spokeswoman says there was "absolutely nothing misleading about his answer" because the meetings were in relation to his role on the Armed Services Committee, rather than as a member of the Trump campaign.
The White House has also backed him, while Republican House Speaker Paul Ryan said there was no evidence that anyone in Mr Trump's campaign had been involved in Russian election meddling.
However, several top Republicans have broken rank to say he should step aside from overseeing the FBI investigation into Russian hacking allegations.
Maine Senator Susan Collins said it would be best if Mr Sessions recused himself from the probe.
US House majority leader Kevin McCarthy told MSNBC's Morning it would be "easier" if Mr Sessions stepped aside, but later reversed his stance on Fox and Friends, saying: "I'm not calling on him to recuse himself".
Republican Senators Marco Rubio, Lindsey Graham and Rob Portman have also said that Mr Sessions should withdraw from the inquiry, reports say.
Republican Representatives Jason Chaffetz, Darrell Issa, Tom Cole, Barbara Comstock and Raul Labrador have agreed.
Many Democrats say Mr Sessions should resign.
House of Representatives Democratic leader Nancy Pelosi said he "lied under oath" and that "anything less than resignation or removal from office is unacceptable".
The American Civil Liberties Union, meanwhile, has called for an investigation into whether Mr Sessions perjured himself.
What does Mr Sessions say?
Speaking to MSNBC on Thursday, he said: "I have not met with any Russians at any time to discuss any political campaign, and those remarks are unbelievable to me and are false."
He added that he would recuse himself from the FBI investigation "whenever it's appropriate", without providing more details.
There is a new inquiry. What is it about?
News of Mr Sessions' meetings broke just after a congressional committee agreed to an investigation into Russia's alleged interference.
The House intelligence panel inquiry will scrutinise contacts between Donald Trump's presidential campaign and Moscow.
The White House denies any improper behaviour during the election campaign, and Russia has consistently rejected allegations of interference.
Russia's foreign ministry spokeswoman has dismissed the latest press reports as "the manifestation of some kind of media vandalism".
Meetings with US politicians were part of the Russian embassy's "everyday business", she told AP.
How the Russia claims have dogged Trump
May 2016: Reports first emerge of hackers targeting the US Democratic Party. Over the next two months, reports suggest US intelligence agencies have traced the breaches to Russian hackers.
July 2016: Jeff Sessions meets Russia's envoy to the US Sergei Kislyak and several other ambassadors at an event on the sidelines of the Republican National Convention.
August 2016: Paul Manafort, Donald Trump's campaign manager, quits after an FBI investigation into his alleged ties to Russian interests in Ukraine and the US.
September 2016: Senator Sessions has a private meeting in his office with Mr Kislyak. The justice department says all meetings were linked to his work on the armed services committee.
October 2016: The US intelligence community release a unanimous statement formally accusing Russia of being behind the hacking of the Democratic Party. Mr Trump questions the findings. Over the coming months, more reports on the hacking emerge. The US intelligence agencies, the justice department and four Congressional committees are all currently investigating the allegations.
February 2017: Mike Flynn resigns as Mr Trump's new national security adviser after it emerges he discussed the potential lifting of sanctions against Russia with Mr Kislyak and then misleading Vice-President Mike Pence about the communication.