Some candidates backed steps to remove the president for the first time, while others ratcheted up their push for Congress to act.
ADVERTISEMENTSen. Cory Booker on Wednesday called on Congress to "immediately" begin impeachment proceedings against President Donald Trump, adding to a growing chorus from 2020 Democratic presidential candidates.
The New Jersey senator, who'd previously said it was too soon to talk about removing the president, tweeted that "Robert Mueller's statement makes it clear: Congress has a legal and moral obligation to begin impeachment proceedings immediately."
"I've been asking for Mueller's testimony — today he made his views clear," Booker added.
Mayor Pete Buttigieg, who previously said he thought it was time for Democrats in the House to start moving toward impeachment, also came out more forcefully after Mueller spoke at the Justice Departmentsaying it's Congress's role to accuse a president of wrongdoing.
"The message really is, 'Over to you, Congress,'" Buttigieg told NBC News in an exclusive interview.
"What he reminded everyone was he's part of a DOJ that says you can't, which means his option wasn't charge or don't charge," he said. "But procedures do exist for a sitting president to be held accountable, and if the Justice Department can't charge a sitting president with an actual crime, then it goes over to Congress to decide whether to charge the president with a high crime. This is as close to an impeachment referral as you could get under the circumstances."
Sen. Kamala Harris also interpreted Mueller's statement as an "impeachment referral."
"We need to start impeachment proceedings. It's our constitutional obligation," Harris tweeted.
"I think it's a fair inference from that press conference that Bob Mueller was referring impeachment to the United States Congress," she told NBC News before an event in South Carolina.
"We have got to now let the process start its course around Congress acting on what we know is essentially indictable evidence and information."
Sen. Elizabeth Warren — the first call for Trump to be impeached after reading Mueller's report — said on Wednesday "it's up to Congress to act."
Former Rep. Beto O'Rourke, who'd also already called for beginning the impeachment process, tweeted, "There must be consequences, accountability, and justice. The only way to ensure that is to begin impeachment proceedings."