Watch Live: With Comey Out, Acting FBI Director Faces Senate Intel Committee

Updated: 11:22 a.m. ET

The absence of former FBI Director James Comey loomed large over the Senate Intelligence Committee's hearing with top U.S. intelligence leaders, but his temporary replacement, now-acting FBI Director Andrew McCabe, assured lawmakers he would not bend to pressure from the White House.

"You cannot stop the men and women of the FBI from doing the right thing, protecting the American people and upholding the Constitution," McCabe said.

Vice Chairman Mark Warner, D-Va., underscored that Comey's absence was atop his mind and that he had plenty of questions for McCabe and the other intel leaders about the ongoing probe into Russian involvement in the 2016 elections.

"It's hard to avoid the conclusion that the president's decision to remove Director Comey was related to the Russia investigation," Warner said, "and that is truly unacceptable."

McCabe assured Warner that he would alert the committee if anyone tried to influence the FBI probe into possible ties between Russia and the Trump campaign.

Chairman Richard Burr, R-N.C., made clear in his opening statement that he wanted the hearing to be about more than just Russia and reiterated there are other global threats of concern, too. But questions of Russia and the ongoing investigation have so far largely dominated the hearing.

In his own first question to McCabe, Burr asked the acting FBI director about one of the more puzzling and surprising statements in Trump's termination letter to Comey — that the law enforcement chief told the president on three separate occasions that he was not under investigation in regards to Russia.

"Sir, I can't comment on any conversations the director may have had with the president," McCabe responded.

While Trump has continued to cast doubt on the intelligence community's findings that Russia did seek to influence the U.S. elections to benefit his campaign, the intelligence leaders were unanimous in their assessment that Russia had indeed interfered with the election.

Director of National Intelligence Dan Coats was unequivocal in his conclusion that there was meddling in his written testimony submitted to the committee:

Moscow has a highly advanced offensive cyber program, and in recent years, the Kremlin has assumed a more aggressive cyber posture. This aggressiveness was evident in Russia's efforts to influence the 2016 US election, and we assess that only Russia's senior-most officials could have authorized the 2016 US election-focused data thefts and disclosures, based on the scope and sensitivity of the targets.

Also joining McCabe and Coats on the panel are: CIA Director Michael Pompeo, NSA Director Adm. Michael Rogers and the heads of the Defense Intelligence Agency and the National Geospatial-Intelligence Agency.