Former vice president Joe Biden speaks during a rally with union members in Pittsburgh on Monday. (Gene J. Puskar/AP)

Former vice president Joe Biden said in an interview broadcast Tuesday that Congress would have “no alternative” but to impeach President Trump if his administration seeks to block its investigations of issues raised in the special counsel’s report on Russian election interference.

Appearing on ABC’s “Good Morning America,” Biden said that the report by special counsel Robert S. Mueller III left several unanswered questions related to whether Trump obstructed the nearly two-year probe, and he argued that Congress should follow up.

“What the Congress should do and they are doing is investigate that,” Biden said. “And if in fact they block the investigation, they have no alternative to go to the only other constitutional resort they have: impeachment.”

“My job in the meantime is to make sure he’s not back as president of the United States of America,” added Biden, who formally launched his bid for the Democratic presidential nomination last week.

Biden’s comments came during a wide-ranging interview in which he also continued to grapple with controversies over his affectionate, physical style with women and his handling of Supreme Court Justice Clarence Thomas’s 1991 Senate confirmation hearing. He also declined to say whether he would pick a woman as his running mate.

Frustration has been building among House Democrats as the Trump administration refuses to cooperate with an array of congressional inquiries, including several related to the Russia report. Attorney General William P. Barr has threatened not to show up at a scheduled Thursday hearing in the House to address how he handled Mueller’s findings.

Mueller’s report did not find sufficient evidence to bring charges of criminal conspiracy with Russia against Trump or anyone associated with his campaign. It did not offer a conclusion on whether Trump obstructed justice.

Barr later concluded that there was not sufficient evidence for obstruction of justice. But Biden said in the ABC interview that are “about seven or eight things that are left undone” related to possible obstruction that Congress should pursue.

The interview aired on the same day that a new poll found Biden opening up a lead in the crowded Democratic presidential field.

In the poll released by CNN, 39 percent of voters who identify as Democrats or Democratic-leaning independents say Biden is their top choice for the nomination. His nearest competitor, Sen. Bernie Sanders (I-Vt.), got 15 percent of support in the poll.

The poll also showed the race remaining fluid, with only about a third of potential Democratic voters saying they would definitely support their preferred candidate.

A Washington Post-ABC poll conducted mostly before Biden’s announcement also suggested there is room for other candidates to grow. It found that over half of Democratic-leaning adults had no preference for the party’s nomination when asked an open-ended question that did not name any candidates, though Biden held a slight edge among those who did.

As he prepared to campaign in Iowa on Tuesday for the first time since his announcement, Bide also released a new video that heavily features former president Barack Obama — whose endorsement Biden has said he did not seek.

The video opens with Obama praising his then-vice president in January 2017 as he bestowed Biden with the Presidential Medal of Freedom, the nation’s highest civilian honor. Obama calls Biden “an extraordinary man with an extraordinary career in public service.”

In the ABC interview, Biden said he was “really proud” of his service in the Obama administration but that he is not running for a third Obama term.

“It’s a new time, it’s a new day,” Biden said.

Biden also continued to try to move past the controversy over how he has interacted with women, publicly touching them in ways that some have said made them feel uncomfortable.

“I’ve always thought that part of leadership, part of politics was listening to people, hearing them, making them feel comfortable,” Biden told co-anchor Robin Roberts in an interview, which was recorded Monday. “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.”

Sitting beside him, Jill Biden defended her husband, saying she had not heard negative stories in the 44 years they have known one another. But she also acknowledged his judgment needs to improve.

“I think what you don’t realize is how many people approach Joe, men and women, looking for comfort or empathy,” Jill Biden said. “But going forward, I think he’s going to 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 also said that he takes “responsibility” for how Anita Hill was treated when she testified about alleged sexual harassment before the Senate Judiciary Committee during 1991 hearings over Thomas’s nomination to the Supreme Court.

“I believed her from the very beginning, but I was chairman. She did not get a fair hearing. She did not get treated well. That’s my responsibility,” Biden said. “As the committee chairman, I take responsibility that she did not get treated well. I take responsibility for that.”

During the interview, Biden said he has a different take on Trump’s “Make America Great Again” slogan, made famous during his 2016 campaign.

“Make America Moral Again,” Biden said. “Return to the essence of who we are, the dignity of the country, the dignity of people, treating our people with dignity. . . . End this God-awful deliberate division that’s being taken … separating people to aggrandize his own power.”

Scott Clement contributed to this report.