Speaking to Fox News' Maria Bartiromo yesterday, the senator said, "I want to understand how all this crap started," and claimed that Senate Intelligence Committee Chairman Richard Burr (R-NC) will call the "whistleblower" for questioning.

He said that investigations into the whistleblower and former Vice President Joseph R. Biden's dealings in Ukraine, two issues at the heart of the impeachment charges against Mr. Trump, will continue to be investigated by the Senate after the president's impeachment acquittal that is expected this week on charges of abuse of power and obstruction of Congress.

The impeachment stemmed from the whistleblower allegation that Mr. Trump pressured Ukraine, including withholding nearly $400 million in military aid, to investigate the Bidens and Ukraine meddling in the 2016 U.S. election.

"If the whistleblower is a former employee of [or] associate of Joe Biden, I think that would be important. If the whistleblower was working with people on Schiff's staff that wanted to take Trump down a year-and-a-half ago, I think that would be important. If the Schiff staff people helped write the complaint, that would be important."