WASHINGTON — In the heat of Texas’s contentious Senate race, a super PAC supporting Texas Attorney General Ken Paxton has launched a scathing new attack ad against incumbent Senator John Cornyn. The ad accuses Cornyn of “betraying” former President Trump, as both candidates vie for Trump’s endorsement ahead of the May 26 runoff.

The advertisement from Lone Star Liberty PAC asserts, “John Cornyn betrayed President Trump but assisted Joe Biden in appointing the most corrupt attorney general in history,” referring to Merrick Garland. The ad’s narrator continues, highlighting Cornyn’s past actions.

It goes on to criticize Cornyn for defending prosecutor Jack Smith and attributing blame to “President Trump, himself.” The ad accuses Cornyn of attacking House Republicans for probing into Manhattan DA Alvin Bragg’s allegations and of supporting former FBI Director James Comey.

Rewind to 2023, when Cornyn expressed his doubts about Trump’s ambitions for the GOP nomination. He told reporters: “I think President Trump’s time has passed him by,” reflecting a broader Republican dissatisfaction following underwhelming results in the 2022 midterms, where several Trump-backed candidates fell short.

During that period, Cornyn also commended Nikki Haley, a 2024 GOP presidential contender, who posed the most significant challenge to Trump’s candidacy. Her campaign was seen as a beacon for those seeking alternatives within the party.

The Lone Star Liberty PAC further targeted Cornyn for his vote in favor of confirming Merrick Garland, Biden’s attorney general nominee. Cornyn had lauded Garland for his pledge to “keep politics out of the Justice Department,” a stance now under scrutiny from his opponents.

Also in 2023, Cornyn called the indictment against Trump for hoarding national security documents “very serious” and noted that the matter was “out of his hands” and for the courts to decide.

The attack ad further spotlighted Corny calling Comey “a good and decent man” while nudging House Republicans not to get too bogged down defending Trump after he was indicted by Bragg on charges of falsifying business records.

“After saying for two weeks he would win without a runoff, Ken Paxton finished second in the primary and as a result he’s now desperately attacking Sen. Cornyn,” senior Cornyn campaign adviser Matt Mackowiak told The Post in response to the ad.

“Texans know the facts: Sen. Cornyn was the Senate vote counter who passed President Trump’s legislative agenda in the first term, and he has voted with him 99.3% of the time while he’s been President,” Mackowiak added.

“Ken Paxton has massive baggage due to his many ethical failings and outrageous personal conduct, and he risks the entire statewide ballot if he is the nominee.”

Cornyn narrowly received the most votes in the March 3 primary, but came up short of the majority support needed to win the GOP nomination outright.

Shortly after the primary, rumors spread that Trump was on the verge of endorsing Cornyn, leaks which reportedly agitated the president.

After Trump announced last week that he would ask whichever candidate he didn’t endorse to leave the race, Paxton said he would be willing to drop out if Senate Republicans agreed to roll back the filibuster and pass Trump’s prized SAVE America Act, which would require proof of citizenship to vote in federal elections.

On Wednesday, Cornyn penned an op-ed for The Post calling for a weakening of the filibuster to pass the SAVE America Act and end the shutdown of the Department of Homeland Security.

Later that day, he went viral when confronted by an NBC reporter about his past support for the filibuster, with the senator responding by waving his hand in the camera and telling her: “I think we’re through, go away.”

Senate GOP leadership, the National Republican Senatorial Committee (NRSC), and Trump’s senior 2024 campaign adviser Chris LaCivita have all pushed the president to back Cornyn, who they say is more electable and whose nomination would free up Republicans to spend money elsewhere.