By Steve Holland and Patricia Zengerle
WASHINGTON (Reuters) - Senior Republicans issued their boldest challenge yet to U.S. President Donald Trump on Wednesday, promising to get to the bottom of the relationship between his aides and Russia, and calling for ousted national security adviser Michael Flynn to testify before Congress.
Trump, facing a deepening crisis less than a month into his presidency, sought to focus the attention on what he called criminal intelligence leaks, calling Flynn a "wonderful man" who had been unfairly treated by the media.
Senator Bob Corker, chairman of the Senate Foreign Relations Committee, and other senators in Trump's party pushed for more information as the White House becomes engulfed by questions about contacts between Trump's team and Russia.
The New York Times reported on Tuesday that phone call records and intercepted calls showed members of Trump's presidential campaign and other Trump associates had repeated contacts with senior Russian intelligence officials in the year before the Nov. 8 election in which Trump defeated Democrat Hillary Clinton.
Democrats demanded an independent investigation of possible illegal communications between Flynn and the Russian government and any efforts by Flynn or other White House officials to conceal wrongdoing. The Democrats called for either a special counsel appointed by the Justice Department or the creation of a bipartisan commission with subpoena power.
Flynn was abruptly forced out by Trump on Monday after revelations that he had discussed U.S. sanctions on Russia with the Russian ambassador to the United States, before Trump took office, and that he had later misled Vice President Mike Pence about the conversations.
The drama of Flynn's departure was the latest in a series of White House missteps and controversies since Trump was sworn in on Jan. 20.
"Let's get everything out as quickly as possible on this Russia issue," Corker told MSNBC's "Morning Joe" program.
"I would want to make sure, with all of this suspicion, that everybody fully understood what has taken place. Otherwise, maybe there's a problem that obviously goes much deeper than what we now suspect," Corker added. Corker expressed alarm over the way the administration is functioning, asking, "Is the White House going to have the ability to stabilize itself?"
In Twitter posts on Wednesday, Trump called the reported Russian connection with his campaign team nonsense, adding, "The real scandal here is that classified information is illegally given out by 'intelligence' like candy. Very un-American!"
At a joint news conference later with Israeli Prime Minister Benjamin Netanyahu, Trump charged that intelligence leaks to the news media were "a criminal act." He said Flynn, a retired U.S. Army lieutenant general, was "a wonderful man" who has been treated "very, very unfairly by the media."
White House spokesman Sean Spicer said on Tuesday that Trump's eroding level of trust in Flynn after a series of "questionable instances" is what "led the president to ask for General Flynn's resignation."
In his comments at the news conference Trump did not address the accuracy of the material he said was being leaked.
Spicer on Tuesday denied there had been any contact between any member of Trump's campaign team and Russia. 'VERY DISTURBING'
Senator Lindsey Graham of South Carolina, a prominent Republican voice on foreign policy who has been a Trump critic, called for a broader bipartisan congressional investigation, to be conducted by a special committee, if it turns out that Trump's presidential campaign communicated with the Russians.
"If it is true, it is very, very disturbing to me. And Russia needs to pay a price when it comes to interfering in our democracy and other democracies, and any Trump person who was working with the Russians in an unacceptable way also needs to pay a price," Graham told ABC's "Good Morning America."
From early on in his White House bid, Trump said that he would like improved relations with Russian President Vladimir Putin, a stance criticized by Democrats and also by some Republicans concerned about Washington softening its stance after Russia's annexation of Crimea from Ukraine and aggression in Syria.
U.S. intelligence agencies previously concluded that Russia hacked and leaked Democratic emails during the election campaign as part of efforts to tilt the vote in Trump's favor.
Corker called the leaks to the news media a mere "sub-issue," saying the main issue was "getting to the bottom of what the Russian interference was and what the relationship was with associates of the Trump effort."
Flynn's testimony before Congress "would be a very appropriate thing for us to have happen," he said.
Senate Majority Leader Mitch McConnell and House of Representatives Speaker Paul Ryan both dismissed the need for the creation of a special committee to look into the matter but promised the Republican-led Congress would move ahead in existing committees.
House Democratic leader Nancy Pelosi called on the FBI to expedite an investigation into the financial, personal and political ties of Trump and members of his administration to the Russians.
The Trump administration has offered the national security adviser job to U.S. Navy Vice Admiral Robert Harward, said two U.S. officials familiar with the matter. It was not immediately clear if Harward, a former deputy commander of U.S. Central Command, had accepted the offer, according to sources.
The Times, citing current and former U.S. officials, said U.S. law enforcement and intelligence agencies intercepted the communications around the same time they discovered Russia was trying to disrupt the presidential election by hacking into the Democratic National Committee.
Reuters could not immediately confirm the Times report, which the Kremlin dismissed as groundless. CNN also reported that Trump advisers were in constant contact with Russian officials during the campaign.
Flynn's conversations with the Russian ambassador took place after the election, around the time that then-President Barack Obama imposed new sanctions on Russia on Dec. 29, charging that Moscow had used cyber attacks to try to influence the election. (Additional reporting by Rick Cowan, Susan Heavey and Julia Harte; Writing by Will Dunham; Editing by Mohammad Zargham and Frances Kerry)