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But court filings unsealed last week, paired with new details about President Donald Trump's own knowledge of events, indicate a wide circle of advisers were aware that Flynn raised the issue when he spoke by phone to Moscow's envoy -- even as Pence reportedly remained in the dark.

The new questions raised by special counsel Robert Mueller's investigation signal what could be a pivotal moment in Pence's careful calibration of trying to keep a safe distance from the Russia probe even while maintaining his credibility for being left out of the loop by the West Wing.

Pence -- who was in charge of Trump's transition -- knew Flynn had contacted Russia, but was left unaware of the sanctions discussion, according to transition officials. It's led to anxiety within Pence's circle that he'll eventually be called to sit for an interview with Mueller.

"They are preparing for that," a person in Pence's orbit said, a sentiment echoed by another source close to the Vice President: "Chairing the transition would make it possible regardless of who it was."

Pence's spokeswoman pushed back on the notion his office is preparing for a potential interview.

"Nothing could be further from the truth. The vice president is focused on passing the largest tax cut in American history," Alyssa Farah, Pence's press secretary, told CNN on Tuesday.

Lawmakers also say Pence owes them answers on what he knew at the time.

"I think he has new questions to answer," said Sen. Richard Blumenthal, a Connecticut Democrat, who said he wanted Pence to appear before the Senate Judiciary Committee to explain what he knew at the time about Flynn's conversations with Russian officials.

In the days since Flynn's guilty plea was unveiled last week, seven people close to the vice president continue to maintain that Pence did not know Flynn spoke with Kislyak about Russian sanctions, despite being the head of the Trump transition.

But among top transition officials, Pence would have been largely alone in his lack of knowledge. According to court filings released last week, Flynn spoke with "senior members of the Presidential Transition Team" about his conversations with Kislyak regarding the new US sanctions.

And Trump himself was told in January by the White House's chief lawyer that Flynn had misled the FBI and lied to Pence about his conversations with Kislyak. Flynn was fired on February 13.

Political chops

An establishment Republican who served for 10 years as a US representative prior to serving as Indiana governor, Pence is among the most politically experienced members of Trump's administration, and has taken on a wide swath of responsibility, including maintaining relationships on Capitol Hill and making frequent trips abroad.

But despite of -- or perhaps because of -- his political acuity, Pence has remained largely oblivious to contacts between Trump officials and Russian operatives, at least according to his aides.

Aside from the Flynn episode, Pence's aides said he did not know Donald Trump Jr. met with a Russian lawyer who claimed to have damning information about Hillary Clinton. And his office similarly claimed that Pence wasn't aware of Trump Jr.'s contact with WikiLeaks in the closing days of last year's presidential campaign. The President's son is set to meet with congressional investigators Wednesday.

In multiple conversations with CNN, the officials sought to explain Pence's role in the transition, his reaction to the news that Flynn had lied to him and why he wasn't aware of Flynn's actions.

A former senior transition official explained that Pence was mostly concerned with "human resources" and personnel in his role as transition chairman, which included oversight of major Cabinet appointments. Another adviser to the vice president said he was focused on interviewing candidates for Senate-confirmable posts.

Two senior transition officials mentioned to CNN that Pence was slowly weened off of email during the transition period, another step to prepare him for his new role as vice president. One of the officials says that Pence's team actively tried to protect him from the various characters in Trump Tower and transition offices during that time period.

"We definitely tried to cut down on the unfettered access folks had to him but it was more about allowing him to focus on the task at hand," this official said.

Transition roles

On the multiple days last December when Flynn was speaking with Kislyak, Pence was thousands of miles away, according to his travel records and a senior transition official at the time, conducting transition meetings in Washington and preparing for his son's wedding in Indianapolis, where he was also busy packing up his home to move to Washington.

One senior White House official said that while there was "some" interaction between Pence and Flynn during the transition, it was not "extensive."

"Mike was coming up with the process for filling Cabinet posts. The Flynn thing was out of his hands -- he's been on the campaign from the start," this official said when asked about Pence's level of trust in the incoming national security adviser.

It's that argument -- Pence was more of a newcomer than Flynn -- that people close to the vice president say bolsters his claim that he didn't know about the extent of these Russian calls. Yet that explanation will surely be tested anew as Mueller's probe reaches closer to Trump's inner circle.

Trump's national security team, who operated out of a conference room in Trump Tower, was based in New York during the transition, while Pence increasingly spent more time in Washington at the presidential transition offices blocks away from the White House. He even took up temporary residence at a house in Chevy Chase while Trump continued to live in his Manhattan apartment.

Two transition officials who prepared the vice president for his television appearance on January 15 said that questions about Flynn and Kislyak were not a surprise.

"We knew Pence would get asked about it," one senior transition official said.

Another transition official said Pence called Flynn on January 14 specifically so he could say during his Sunday show appearances that he'd spoken with the national security adviser about his conversations with Kislyak.

Flynn insisted to Pence did not discuss sanctions with Kislyak, and during his two television appearances, Pence readily relayed that information -- which turned out to be a lie. Pence discovered that Flynn lied to him through media reports on February 9 as The Washington Post reported that Flynn had in fact spoken with Kislyak about Russian sanctions.

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Russia probe tests Pence in-the-dark defense - CNNPolitics