Ted Cruz is taking a subtle shot at Marco Rubio in his new campaign ad.

Since the Republican presidential debate on Tuesday, Cruz has been sticking to some familiar talking points about immigration. His latest campaign ad, which debuted on Iowa television Friday morning, hews to that narrative almost perfectly.

“Securing our border and stopping illegal immigration is a matter of national security,” Cruz tells the camera, his brow furrowed. “That’s why I fought so hard to defeat President Obama and the Republican establishment’s Gang of Eight amnesty plan. Their misguided plan would’ve given Obama the authority to admit Syrian refugees, including ISIS terrorists. That’s just wrong.”

The message is designed as a subtle hit on Rubio, who masterminded the comprehensive immigration reform bill two years ago. In one fell swoop, the ad links Cruz’s rival to amnesty, the Republican establishment, and a plan that would have, according to Cruz at least, welcomed ISIS terrorists to the United States with open arms—everything Rubio is desperately trying to avoid. 

The ad is particularly clever in that Cruz manages to avoid taking Rubio on directly. As Harvard professor Stephen Ansolabehere told me last week, negative campaigning can be risky with several credible candidates still vying for the nomination. This way, Cruz can make Rubio look bad without potentially alienating voters.