"It led me to believe the walls are closing in and they've been notified by counsel of some actions about to happen", a senior Republican official told Politico.
Mueller had signaled a willingness to accept written answers on matters of collusion.
Trump's lawyers counseled him strongly not to agree to sit down with Mueller and investigators in person, although the president has never publicly ruled out that he might do so.
The Trump administration is growing increasingly anxious and bracing for a slew of indictments as a result of the special counsel Robert Mueller's investigation into the Trump campaign's ties to Russian Federation, according to a new Politico report.
Trump's latest Cabinet reshuffles and Twitter rants also appear to reflect a growing concern about the investigation.
What did the president say?
Democrats and a number of Republicans have raised concerns about Whitaker's appointment, with a bipartisan group of US senators renewing a push for legislation to protect the special counsel.
Trump had huddled with lawyers at the White House this week but made clear: "my lawyers don't write answers, I write answers".
"You can see it in Trump's body language all week long". They are a disgrace to our Nation and don't.care how many lives the (sic) ruin.
Trump also was asked Friday about his recent tweets, which seemed to betray a sense of frustration, where he called the Mueller probe "illegal" and said, without evidence, that Mueller's team was shouting at defendants. It was reminiscent of his admission to NBC's Lester Holt a year ago that he ousted James Comey as FBI director to kill the investigation.
That Trump's admission about Whitaker to The Daily Caller and his tweetstorm came after this series of developments on the Russian Federation front could indicate that the president is growing increasingly anxious about what Mueller has.
Former New York mayor Rudy Giuliani backs Donald Trump at a rally on October 10, 2016 in Ambridge, Pennsylvania.
Jeffrey Cramer, a longtime former federal prosecutor who spent 12 years at the DOJ, echoed that assessment.