WASHINGTON — Sen. Ted Cruz has been peddling a conspiracy theory for weeks suggesting that the FBI incited last year’s attack on the U.S. Capitol.

In this scenario, the nation’s prime law enforcement agency prodded supporters of defeated president Donald Trump to ignore police lines, assault officers, smash through doors, turn flagpoles into spears, invade the Senate chamber and threaten the vice president and House speaker.

No evidence has surfaced for this explosive theory. And the purported motives for such a conspiracy are murky.

The FBI director, under oath two months after the Jan. 6, 2021, riot, ruled out that there were “fake Trump protesters” of any kind in the mob. Another top FBI official told Cruz at a hearing last month that no federal agents incited violence.

That has not deterred the two-term Texas Republican from persisting with the “false flag” theory.

“If the federal government was actively encouraging illegal conduct, was actively encouraging violence,” Cruz said on an episode of his podcast devoted to the so-called fed-surrection theory, “that is incredibly concerning, because it is an abuse of power.”

The key word there is “if.”

Cruz has offered no evidence the FBI has done anything wrong — an allegation-by-insinuation approach that critics view as demagoguery.

His office sidestepped requests to provide any factual basis for the claims. Instead, an aide pointed to comments from Cruz that ignore the FBI’s denials and put the onus on the bureau to disprove baseless allegations.

“I asked the FBI over and over and over again: Did FBI agents commit acts of violence on January 6? The FBI refused to answer that question,” Cruz said on his Jan. 14 podcast. “I asked, did they incentivize? Did they incite? Did they urge others to commit acts of violence? Again, the FBI refused to answer.”

The theory is full of contradictions.

Throughout his presidency, Trump complained that the FBI was working against him. Why would this purported “deep state” want to derail Joe Biden’s victory and prolong Trump’s time in power?

Cruz and others who promote it have not explained why the FBI would be on both sides — hunting down rioters, yet also encouraging sedition and trying to overturn the election.

“He is lying for the sake of getting power. It’s a very cynical game,” said Russell Muirhead, a Dartmouth College political scientist who co-authored a book on innuendo in the Trump era titled A Lot of People are Saying. “I’m absolutely certain he does not believe it. Ted Cruz has an IQ that’s way beyond what most of us could ever aspire to.”

Trump, who exhorted followers to “fight like hell” to stop Congress from certifying the election, promoted the false flag theory at an Arizona rally last month.

“Exactly how many of those present at the Capitol complex on Jan. 6 were FBI confidential informants, agents or otherwise, working directly or indirectly with an agency of the United States government? People want to hear this,” he told thousands of supporters.

‘Who is Ray Epps?’

Cruz didn’t begin to point a finger at the FBI until a full year after the riot.

At a hearing the day before the anniversary, he called the event a “violent terrorist attack.”

That did not play well with right-wing commentators and others who downplay the violence and want to deflect blame away from Trump.

Cruz shifted into damage control mode, starting on Tucker Carlson’s prime-time Fox News show the night of the anniversary.

The senator expressed remorse for using the same language as Democrats to describe the riot, emphasizing that he only views attacks on police as acts of terrorism.

Carlson accused the senator of lying, given he’d used the term at least 17 times in the past year.

Then Carlson — enormously influential among Trump supporters and a gatekeeper to the 2024 Republican nomination that Cruz covets — broached a pet theory that puts a man named Ray Epps at the center of the false flag scheme.

Cruz played along. It was apparently the first time he publicly embraced the theory.

“For him to appear on the FBI’s most wanted list and come off, it certainly suggests he was working for the FBI. That’s not conclusive, but that’s the obvious implication,” Cruz told Carlson.