Congressional Republicans have announced parallel inquiries into a uranium deal under President Barack Obama and Hillary Clinton's emails.
One committee will investigate how the Obama administration approved a 2010 acquisition that gave Russia control of 20% of the US uranium supply.
Two other panels will scrutinise the FBI decision not to charge Mrs Clinton over her private email server.
Democrats pilloried the inquiries as "a massive diversion".
Both issues to be placed under the spotlight by the committees are longstanding political grievances of President Donald Trump.
His campaign aides are currently the subject of congressional investigations into whether they colluded with alleged Kremlin attempts to sway last year's US presidential election.
On Tuesday, House Judiciary Committee Chairman Bob Goodlatte and House Oversight Committee Chairman Trey Gowdy announced inquiries into the previous administration.
They said there were "outstanding questions" about the FBI's investigation into former Democratic presidential candidate Mrs Clinton's emails.
The congressmen said they wished to know why former FBI director James Comey chose to divulge the inquiry into Mrs Clinton, but not the one about Trump aides and Russia.
Also on Tuesday, Devin Nunes, the Republican chairman of the House Intelligence Committee, announced his panel's inquiry into the sale of a Canadian mining firm that had mines in the American West.
Uranium One - which owned a fifth of US uranium supplies - was acquired seven years ago by Russian state-owned company Rosatom.
Uranium deal to Russia, with Clinton help and Obama Administration knowledge, is the biggest story that Fake Media doesn't want to follow!— Donald J. Trump (@realDonaldTrump) October 19, 2017
The US Department of State, under former Secretary of State Mrs Clinton, helped approve the deal.
The Hill reported last week that at the time of the sale the FBI was investigating alleged attempts by Moscow to gain influence in the US nuclear industry through bribery and extortion.
The Hill and New York Times have reported that Russian nuclear officials and Uranium One's chairman donated millions of dollars to the Clinton charitable foundation.
Mr Nunes told reporters at Capitol Hill on Tuesday: "One of the things we are concerned about is whether or not there was an FBI investigation, was there a DOJ [Department of Justice] investigation and if so, why was Congress not informed of this matter."
President Trump has sought to draw attention to the story, tweeting last week: "Uranium deal to Russia, with Clinton help and Obama Administration knowledge, is the biggest story that Fake Media doesn't want to follow!"
But Democratic congressmen accused Republicans on Tuesday of creating a distraction.
"This new investigation is a massive diversion to distract from the lack of Republican oversight of the Trump administration and the national security threat that Russia poses," said Elijah Cummings and John Conyers in a statement.
Mrs Clinton said in an interview with cable network C-SPAN on Monday that the Uranium One allegations are "baloney".