In addition to setting the April 1 deadline for handing over Mueller's report, Feinstein is also asking Barr to start producing underlying documentation from the investigation on the same day.

Feinstein was one of four lawmakers Barr sent the four-page letter outlining the principal findings of Mueller's investigation to on Sunday. But Democrats immediately clamored for Barr to make the entire report public.

In addition to Feinstein's April 1 deadline, top House Democrats have asked Barr to hand the Mueller report over to Congress by April 2, next Tuesday. The six House committee chairs, in a separate letter on Monday, said Barr's initial summary "leaves open many questions."

Mueller turned his report over to the Justice Department on Friday, signaling the formal end of the two-year investigation.

Mueller, according to the letter, did not uncover evidence that the Trump campaign conspired or coordinated with the Russian government to interfere in the 2016 election.