Vice President Mike Pence on Friday demanded a probe of the FBI for allegedly spying on the Trump campaign in 2016 — calling a report that the bureau sent an undercover agent to gather information from adviser George Papadopoulos “very troubling.”

“We’ve got to get to the bottom of how all this started,” Pence said in an interview on Fox News. “The American people have a right to know how this investigation even began.”

The vice president was responding to a question about a New York Times report that the FBI sent an investigator to meet with Papadopoulos to try to determine if the campaign was working with Russia.

The investigator who met with the adviser at a London bar two months before the election was posing as a research assistant, the Times reported, citing unnamed sources familiar with the operation.

The effort eventually “yielded no fruitful information,” the paper reported, but the revelation may provide further ammunition for President Trump, who has denounced what he has termed “spying” against his campaign.

Attorney General William Barr echoed that characterization in testimony during a Senate Appropriations Committee hearing, saying he would look into the “genesis” of the FBI probe into Russian interference in the 2016 election that was later taken over by special counsel Robert Mueller.

The 22-month investigation led to charges against 34 people, including Papadopoulos, who pleaded guilty to lying to the feds and pledged to cooperate, eventually serving 12 days behind bars.

“As the attorney general said when he testified before Congress, there was spying,” Pence said Friday. “We need to understand … whether there was a sufficient predicate. We need to get to the bottom of how this all began and if there was a violation of the rules, if the law was broken, the people that were responsible need to be held accountable.”

The vice president also defended Barr’s decision to blow off testifying before the House Judiciary Committee a day after he was questioned by members of its Senate counterpart.

The AG told the House committee Wednesday that he wouldn’t attend the hearing to testify about Mueller’s report on the Russia probe because he only wanted to be questioned by members of the panel, not also by staff attorneys.

On Friday, Pence noted that when he served in the House, he sat on the Judiciary Committee for 11 years and could not recall an instance when staff lawyers were required to ask questions of a witness along with House members.

“Members of Congress should all do their job and ask questions,” he said.