There's a giant problem with Bill Barr's claim that Trump's campaign was being spied on

Attorney General William Barr suggested the FBI and intelligence agencies were "spying" on the Trump campaign -- but there's a major flaw in that conspiracy theory.

Barr made the explosive allegation -- which matched President Donald Trump's claims -- under questioning by Sen. Jeanne Shaheen (D-NH), but he later admitted he had "no specific evidence" of wrongdoing by the Justice Department he now oversees, reported the Washington Post.

Trump has long questioned the origin of the investigation into Russian election interference, and he and his allies claim the FBI improperly conducted surveillance of his campaign.

They've largely based those claims on the Foreign Intelligence Surveillance Act warrant granted to monitor former Trump campaign adviser Carter Page and the activities of an informant who was later identified as Cambridge University professor Stephan Halper.

The American Halper met several times with Page and former Trump campaign adviser George Papadopoulos, who later pleaded guilty to lying to FBI agents about this Russian contacts, to discuss foreign policy during the summer and fall in 2016.

The FISA warrant was granted after Page left the campaign, and the FBI had been watching him since well before he joined the campaign.

Former director of national intelligence James Clapper flatly denied the FBI had been spying on Trump's campaign, but he agreed some Trump campaign associates were caught up in surveillance efforts -- against Russia.

“They were spying on — a term I don’t particularly like — but on what the Russians were doing,” Clapper said last year.

U.S. law enforcement and intelligence agencies were gathering information about Kremlin efforts to influence the 2016 election, and some contacts between Russians and Trump campaign associates were swept up as part of those efforts.

"There was clearly an information-gathering effort going on. The surveillance we know about came after Page was off the campaign. From there, the question is whether you consider hiring an informant to talk to a couple of Trump campaign advisers to be 'spying on a political campaign," wrote the Washington Post's Aaron Blake.

"Clapper suggests that, even if you do consider it 'spying,' the target was Russia and not the campaign."

Barr admitted that surveillance and other investigative efforts may have been conducted lawfully, but his call for an investigation of alleged "spying" lends credibility to Trump's claims -- and helps delegitimize whatever evidence special counsel Robert Mueller found.