A U.S. Senate panel is taking a new look Monday into the extent of Russian meddling in last year’s presidential election, even as President Donald Trump continues to dismiss Moscow’s interference.

The Senate Intelligence Committee is hearing testimony from Sally Yates, who was briefly acting attorney general, the country’s top law enforcement official, in the early days of the Trump administration before the new president fired her.

She had been a key Justice Department official under former president Barack Obama and is expected to answer questions about warnings she gave the incoming administration about discussions that Michael Flynn, the retired Army general Trump had named as his national security adviser, was having with Russia’s ambassador to Washington.

Flynn served only 24 days in the key White House post before Trump fired him after U.S. intercepts of Flynn’s conversations with Sergey Kislyak showed that Flynn had lied to Vice President Mike Pence and others about his contacts with the Russian diplomat. Yates feared that as a result of his denial of the contacts, Flynn might be vulnerable to blackmail.

In addition, James Clapper, Obama’s director of national intelligence, is expected to testify. He was instrumental in the U.S. intelligence community’s conclusion that Russia sought to boost Trump’s chances of winning by hacking into the computer of the campaign chief for his opponent, former U.S. Secretary of State Hillary Clinton.

WikiLeaks’ role

The anti-secrecy group WikiLeaks subsequently released thousands of emails in the weeks before the election that showed embarrassing behind-the-scenes Democratic operations aimed at helping Clinton win her party’s presidential nomination.

Clinton last week partly blamed her upset loss to Trump on the daily release of the emails just before the November election.

Trump, not wanting to give credence to any election happenstance that might undermine the legitimacy of his victory, continues to downplay the congressional investigations of Russian meddling and a probe by the Federal Bureau of Investigation, the country’s top law enforcement agency, into whether Trump campaign aides colluded with Russian interests to help him win.

He again last week rejected the official view that Russia hacked into the computer of Clinton campaign chief John Podesta, saying that it “could have been China, could have been a lot of different groups.”

In a Twitter comment, Trump said, “The phony Trump/Russia story was an excuse used by the Democrats as justification for losing the election.”