“Slick, slippery, stealthy: Mitt Romney had us fooled. Posing as Republican, he tried to infiltrate Trump’s administration as Secretary of State,” says the commercial, referring to the president’s past consideration of Romney to be his secretary of state.

“Now his cover’s blown — exposed by news reports as a Democrat secret asset,” the ad’s narrator says. “Sources say Romney’s plotting to take down President Trump with impeachment.”

The commercial concludes with a call to action.

“Tell Romney, quit colluding with Democrats on impeachment,” the narrator says, as the senator’s office phone number flashes on the screen.

A Romney spokesperson declined to comment.

The Club for Growth, which vocally opposed Trump in 2016 and spent millions of dollars on negative ads against him, has since transformed itself into a pro-Trump outfit and is investing a relatively small amount to air the commercial. It will spend just $25,000 on TV and $15,000 on digital, according to a person familiar with the media buy. It remains to be seen whether other conservative groups will go after the Utah senator.

Romney, who was the Republican Party’s 2012 presidential nominee, is one of the few congressional Republicans who has shown a willingness to speak out against the president. Trump has fired back, recently taking to Twitter to call Romney a “pompous ‘ass.’”

The 72-year-old Romney, however, has told friends he cares little about what the president has to say about him. Instead, Romney is moving forward with an aggressive plan to aid Republicans in 2020 Senate races.