'What is the White House afraid of?' Democratic senator asks regarding Mueller probe Sen. Chris Van Hollen said Trump allies should stop trying to undermine Mueller.

 -- The Democrat who heads the party's senatorial campaign committee said Republicans need to end what he called a “concerted effort” to undermine the credibility of special counsel Robert Mueller’s investigation into Russian meddling in the 2016 election.

“I think Republicans should end their concerted effort to undermine the credibility of the Mueller investigation,” Democratic Senatorial Campaign Committee Chairman Sen. Chris Van Hollen, D-Md., told ABC News Chief Anchor George Stephanopoulos in an exclusive interview on “This Week” Sunday.

The Maryland senator also questioned why the White House is concerned about Mueller’s probe.

“The question is, 'What are they afraid of? What is the White House afraid of?' Let's let [the special counsel] finish the job and get the facts,” he said.

Mueller has so far charged four people, including former National Security Adviser Michael Flynn.

When President Trump was asked Friday whether he would consider pardoning Flynn, he said, "I don't want to talk about pardons for Michael Flynn yet.”

After Trump’s comment, White House lawyer Ty Cobb said, "There is no consideration at the White House of any pardon for Michael Flynn."

Similarly, Trump's personal lawyer, John Dowd, in August told USA Today that firing Mueller has "never been on the table."

Sen. Van Hollen on Sunday told Stephanopoulos that he takes the president's team at their word that firing the special counsel Mueller is not under consideration.

“I certainly hope that is the case,” Van Hollen said.

Van Hollen also discussed the GOP tax plan, which Congress is expected to vote on early this week. He slammed the 1,000-page bill as “huge giveaway to big corporations.”

“This is a total betrayal of President Trump's economic populist message on the campaign trail,” Van Hollen said. “Millions of middle-class taxpayers will see their taxes go up, even though Republicans promised that would not happen.”