Joe Biden has warned Donald Trump that, if the president attempts to block Congress from digging deeper into the findings of the Mueller Report, then lawmakers will be forced to start impeachment proceedings.

In a Good Morning America interview broadcast early Tuesday, the frontrunner for the Democratic nomination for president said the Mueller report proved “beyond question” that Russia interfered in the 2016 election.

With the Democratic Party split over the political and electoral impact, Biden signaled that he may add a centrist voice to calls for impeachment proceedings.

He said it was up to the Democrats to step in where Special Counsel Robert Mueller left matters unfinished because he felt he didn't have the authority to investigate or prosecute further. “There are elements of the report, in the second phase of the report—about seven or eight things—that are left undone,” said Biden. “[Mueller] was not within his purview to investigate, he thought. The Congress is attempting to take that up.”

Biden urged Congress to carry on probing deeper into those issues and warned the president that, if he tries to get in the way of that process, he'll be in deep trouble. “If in fact they block the investigation, they have no alternative but to go to the only other constitutional resort they have, [which] is impeachment,” he said.

Biden added: “My job, in the meantime, is to make sure he's not back as president.”

The former vice president was boosted Tuesday morning by CNN/SRRS poll which gave him an 11-point bounce following his candidacy announcement last week, leaving him towering above his Democratic rivals. Thirty-nine percent of Democrats or Dem-leaning independents say he's now their top choice for the nomination, up from 28 percent last month.

However, Biden is still being dogged by one issue. He faced repeated questioning on Good Morning America about his previous over-friendly interactions with women, and was even warned by his wife Jill that he's going to have to change his ways during the campaign period.

“I think what you don't realize is how many people approach Joe. Men and women, looking for comfort or empathy,” said Dr. Jill Biden. “But going forward, I think he's gonna have to judge—be a better judge—of when people approach him, how he's going to react. That he maybe shouldn't approach them.”

Biden agreed, adding: “It's my responsibility to be more sensitive to whether or not someone wants me to reassure them or wants to say hello or wants to show affection toward. And that's my responsibility.”

The former vice president went on to say that he wants his campaign theme to be “Make America moral again,” adding: “[I want to] make America—you know, return to the essence of who we are, the dignity of the country, the dignity of people, treating our people with dignity.”

He refused to be drawn on whether he would select a female running mate—as rival candidate Sen. Cory Booker has done—saying it would be “presumptuous” to make a call on that at this stage.

“If you take a look at most of my staff,” he went on. “I mean, they ... reflect who we are. Men, women, African Americans, Asian Americans, Hispanic, Latino. I mean, so it would be a government that would represent everyone. Who that would be if I were fortunate enough to win ... I haven't made that decision.”

The CNN poll put Biden more than 20 points ahead of his nearest rival, Sen. Bernie Sanders, who holds just 15 percent support. The best-supported woman in the poll was Elizabeth Warren, lagging behind on 8 percent.