By Patricia Zengerle
WASHINGTON (Reuters) - Two officials in former President Barack Obama's administration will testify on Monday in a Senate investigation into allegations of Russian meddling in the 2016 U.S. election and possible collusion between President Donald Trump's campaign and Moscow.
James Clapper, the former director of National Intelligence, and Sally Yates, who was deputy attorney general, will appear before the Senate Judiciary subcommittee on crime and terrorism in the first public testimony by former officials from the Democratic administration in a congressional probe on Russia.
Congressional committees began investigating after U.S. intelligence agencies concluded that Russian President Vladimir Putin had ordered hacking of Democratic political groups to try to sway the election toward Republican Trump, who won an upset victory in November.
Moscow has denied any such meddling. Trump has also dismissed the allegations, suggesting instead that Obama might have wiretapped Trump Tower in New York or that China may have been behind the cyber attacks. He has provided no evidence and neither scenario has been supported by intelligence agencies.
Both officials testifying on Monday have left government: Trump fired Yates from the Department of Justice in January, and Clapper retired on Jan. 20, when Trump took office.
Senator Lindsey Graham, a Russia hawk and sometime critic of Trump, has been one of the leading Republican voices calling for a thorough investigation of Russia and the election.
Yates is expected to tell the senators that on Jan. 26, when she was acting Attorney General, she had warned White House Counsel Don McGahn that Michael Flynn, Trump's then national security adviser, had not told the truth about conversations he had held with Sergei Kislyak, Moscow's ambassador to Washington, about U.S. economic sanctions on Russia.
Flynn resigned after less than a month in office.
Trump has defended Flynn, an early supporter in his election campaign, encouraging him to seek immunity from prosecution and referring to the congressional probes as a "witch hunt" instigated by Democrats sore over their election loss.
Hours before Monday's hearing, Trump insinuated that Yates leaked information on Flynn to the media.
"Ask Sally Yates, under oath, if she knows how classified information got into the newspapers soon after she explained it to W.H. Council. (sic)" Trump wrote in a post on Twitter.
In another post, he noted that Flynn, who was pushed out by Obama from his job as director of the Defense Intelligence Agency, had been granted top security clearance by the Obama administration.
The congressional hearings have been shadowed by allegations, mostly from Democrats, that lawmakers are too partisan to investigate effectively.
Clapper, Yates and another official who served under Obama, former CIA Director John Brennan, had been scheduled to testify to the House of Representatives intelligence committee in March, but that hearing was canceled by the panel's chairman, Republican Devin Nunes.
Nunes, a Trump ally, has since recused himself from the Russia investigation amid concerns that he was too close to the White House to lead a credible probe.
Yates, Clapper and Brennan are now due to appear at a public hearing of the House committee that has not been scheduled.
The Judiciary subcommittee probe is one of three main congressional investigations of Russia and the 2016 U.S. election. The FBI and U.S. intelligence agencies are conducting separate investigations.