On Wednesday morning, while Rubio took to the nation’s television airwaves to hit Cruz, the super PAC supporting Rubio’s candidacy also took aim at the Texas senator. In an email to donors, Conservative Solutions PAC chairmen Warren Tompkins and Jon Lerner spent four paragraphs disparaging Cruz’s debate performance; and then, in the fifth paragraph, looked to draw attention to Cruz’s use of the term “America First,” an isolationist dog whistle to many seasoned political observers, in summing up his foreign policy approach.

“Now, for people who don’t know history, that term is unobjectionable. But Ted Cruz is no dummy,” Tompkins and Lerner write. “He knows what he’s saying when he calls for an “America First” policy. “America First” was the pro-German organization in the 1940s that advocated keeping America out of World War II. It was also the phrase used by Pat Buchanan in his isolationist campaign in 1992.

“Cruz should explain why he is choosing to describe his position in the same way as noted isolationists in American history,” the email continues. “And he should explain why his voting record against our intelligence capabilities and military funding, and his position in favor of anti-American dictators is not in keeping with those harmful chapters in our history.”…

“You know, Ted stood up there and said, ‘I’m gonna utterly destroy ISIS,’ Rubio said Wednesday morning during an appearance on Fox News Channel. “Anyone can say that. What are you gonna do it with? And when you support a budget like he does, that dramatically cuts defense spending, when you vote against every defense authorization bill ever presented before you, how can you argue that the bill that pays for the military, that funds our troops and the Iron Dome, how can you then stand there and say that? ‘I’m gonna utterly destroy ISIS,’ but I’m not gonna pay for or support what it would take to utterly destroy ISIS.”