(CNN) - With a few choice words, special counsel Robert Mueller on Wednesday pushed the 2020 Democratic presidential field closer to agreement on what has been a sharply divisive issue: whether to begin impeachment proceedings against President Donald Trump.
Mueller in his first public comments since beginning -- and ending -- his investigation into Russian interference in the 2016 election again refused to exonerate Trump of obstructing justice, saying, "If we had had confidence that the president clearly did not commit a crime, we would have said so."
The Democratic pile-on began minutes after Mueller concluded his brief remarks. New Jersey Sen. Cory Booker and New York Sen. Kirsten Gillibrand for the first time called on the House to move forward with impeachment proceedings.
Booker said it was a "legal and moral obligation" of Congress. Gillibrand in a statement cited the Trump administration's refusal to fully cooperate with House Democrats and Mueller's words as her reasons for declaring it "time for Republicans and Democrats to begin impeachment hearings and follow the facts wherever they may lead."
Booker and Gillibrand join other primary rivals, like Massachusetts Sen. Elizabeth Warren, an outspoken supporter of congressional action, on the side of pursuing impeachment hearings. It is a decision that has divided Democrats on and off Capitol Hill, where House Speaker Nancy Pelosi has repeatedly warned of a political backlash in explaining her decision to stop short of impeachment.
Pelosi and other Democratic leaders, including some top presidential contenders, are keen for Democratic-controlled House committees to continue pulling at threads related to alleged misconduct by Trump and his allies -- a tactic that would, for now, delay a decision on whether to pursue impeachment.
But Mueller's comments will make the chore that much more difficult.
In a hastily announced public statement, the former FBI director effectively told Congress that his testimony -- which they have sought -- was already out there, in the report filed by his office, and said "a process other than the criminal justice system" would be required "to formally accuse a sitting president of wrongdoing."
Many Democrats interpreted his words as a coded appeal for Congress to escalate the matter.
"I think it's a fair inference from what we heard in that press conference that Bob Mueller was essentially referring impeachment to the United States Congress," California Sen. Kamala Harris, a former prosecutor, said in South Carolina. Pete Buttigieg, the mayor of South Bend, Indiana, echoed that point in a tweet, calling Mueller's words "as close to an impeachment referral as it gets."
An aide to Booker told CNN his decision had been clinched by Mueller's own words.
"Mueller's statement went further than the report," the Booker aide said. "Cory has been moving towards calling for impeachment proceedings due to Trump's continued stonewalling of Congress since the release of the report - combined with (Attorney General William) Barr's misleading statements and only the unredacted report released to the public. Today made it abundantly clear that there is one remedy that Mueller intended here, and that is for Congress to handle it."
Warren, who began making her case for impeachment last month, doubled down on her position -- noting, as she did initially, that a full review of Mueller's report contradicted Trump's claim of "total exoneration" by the special counsel.
"Mueller's statement makes clear what those who have read his report know: It is an impeachment referral, and it's up to Congress to act. They should," Warren tweeted, adding: "Mueller leaves no doubt: 1) He didn't exonerate the president because there is evidence he committed crimes. 2) Justice Department policy prevented him from charging the president with any crimes. 3) The Constitution leaves it up to Congress to act — and that's impeachment."
Former Vice President Joe Biden's campaign offered a more cautious response, saying Congress "must do everything in its power to hold this Administration to account," but stopped short of pushing for an escalation in the House.
"Vice President Biden agrees with Speaker Pelosi that no one would relish what would certainly be a divisive impeachment process, but that it may be unavoidable if this Administration continues on its path," a Biden spokesman told CNN.
Vermont Sen. Bernie Sanders, who has warned that Democrats could suffer in 2020 if they focused too much on Mueller, said he would put his faith in Democratic House leaders.
"Given the reality that we have a president who believes he is above the law, Congress must continue its investigations," Sanders, who has recently signaled an increasing openness to impeachment, tweeted on Wednesday. "If the House Judiciary Committee deems it necessary, I will support their decision to open an impeachment inquiry."
Others in the broad field of 23 have been more direct -- and sharpened their messages after Mueller spoke.
"Robert Mueller made it clear: No exoneration," Washington Gov. Jay Inslee stated in a tweet. A few minutes later, former Housing and Urban Development Secretary Julián Castro said Mueller had "made clear this morning that his investigation now lays at the feet of Congress." Former Rep. Beto O'Rourke in a tweet said the only way to guarantee "consequences, accountability, and justice" was to begin proceedings. And Massachusetts Rep. Seth Moulton, a current House member, said it was now his chamber's duty to push forward.
"Mueller did his job. Now it's time to do ours," Moulton tweeted. "Impeachment hearings should begin tomorrow."
CNN's Rebecca Buck, Arlette Saenz and Kyung Lah contributed to this report
The-CNN-Wire ™ & © 2019 Cable News Network, Inc., a Time Warner Company. All rights reserved.