Democratic presidential frontrunner Joe Biden said in a television interview aired Tuesday that Congress would have “no alternative” but to impeach President Trump if the White House tries to block Democratic-led investigations spurred by special counsel Robert Mueller’s report on Russian election interference.

The former vice president told ABC’s “Good Morning America” that special counsel Robert Mueller’s report left unclear whether Trump obstructed the nearly two-year probe, making it imperative that the Democratic-controlled House probe the matter.

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

The comment from the former vice president comes as Attorney General William Barr has threatened that he may not appear at a hearing scheduled Thursday in the House to address how he weighed Mueller’s finding.

House Judiciary Committee Chairman Jerry Nadler, D-N.Y., who is leading an effort to seek a complete version of Russia special counsel Robert Mueller's inquiry, wants Barr to be questioned by committee staff lawyers in addition to lawmakers. Barr has balked at being question by the committee’s counsel.

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Democrats have sought to question the attorney general about his decision to clear Trump of obstruction of justice after the special counsel's team highlighted numerous examples in which the president attempted to limit or derail Mueller's investigation.

Barr intervened when Mueller declined to express a view on whether Trump's conduct was criminal. On the central question of whether Trump or his presidential campaign conspired with the Russian government to tilt the 2016 election, the special counsel found insufficient evidence to support such a conclusion.

Biden said in the “Good Morning America” interview that are “about seven or eight things that are left undone” related to possible obstruction that Congress should pursue.

Five of Biden’s 20 rivals for the Democratic presidential nomination – Massachusetts Sen. Elizabeth Warren, California Sen. Kamala Harris, Massachusetts Rep. Seth Moulton, former HUD Secretary Julian Castro, and Miramar, Florida, Mayor Wayne Messam – have called on the House to move forward on impeachment proceedings.

Biden stopped well short of the five Democratic hopefuls’ push to immediately move for impeachment, an issue that has divided the Democratic caucus. Biden’s stance is more in line with House Speaker Nancy Pelosi, who has resisted going down the impeachment path because Republicans control the Senate. She, however, left the door open to impeachment proceedings last week, telling House Democrats that "if that’s the place the facts take us, that’s the place we have to go."

Biden said in the GMA interview he’s focused on trying to win the nomination and beat Trump in the general election in 2020.

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

Contributing: Nicholas Wu, Kevin Johnson, and Bart Jansen