If Scott Walker is worried about GOP frontrunner Donald Trump, he has a funny way of showing it. In a new 60-second ad released in preview form exclusively to LifeZette, the Wisconsin Governor takes direct aim at Big Donor fave Jeb Bush.

The ad is shown for the first time here.

https://www.youtube.com/watch?v=Sjze6_Rq-Qo&feature=youtu.be

Walker now joins New Jersey Gov. Chris Christie, who has been citing Bush for being “irrelevant” and “AWOL” during the big conservative struggles of the past six-and-a-half years.

The growing sense among non-Bush campaign professionals is that Bush offers Trump a convenient and powerful foil that starves the rest of the race of exposure. Walker is now joining the attack and clearly hopes to gain attention by taking on the GOP field’s top money raiser.

Walker has been toughening his rhetoric as Trump shows no sign of faltering any time soon.

In recent days Walker has called on Obama to show “some backbone” in his dealings with the Chinese, said building a wall on the border with Canada is “a legitimate issue,” and promised to defeat Islamic militants by “unleashing” the U.S. military.

Walker has been toughening his rhetoric as Trump shows no sign of faltering any time soon.

The ad highlights Walker’s commitment to terminating the Obama administration’s Iran nuclear deal if Congress is unable to stop it. Beginning with a series of foreboding soundbites on the deal’s shortcomings, the ad shows President Obama’s own party in disarray, before moving on to Bush.

In the video, Jeb Bush is asked what he would do about the deal on Day One if he’s elected president.

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“You will rip up the agreement … if you become president?” an audience member suggests.

“I’ll certainly look at it,” Bush responds, a sharp contrast to Walker’s announcement speech promise to repeal the nuclear agreement with Iran on his “very first day in office.”

Related: Joyless Jeb

This isn’t the first time Walker and Bush have scuffled over their opposing approaches to handling the controversial deal. Last month, Bush threw the first punch during a town hall meeting in Nevada in which he portrayed Walker as naive for his promise to terminate the deal on his first day in office.

“One thing that I won’t do as a candidate is say, ‘I’m going to tear up the agreement on day one,’” Bush says.

Walker uses the line against Bush by running it in his new ad, which is entitled “On Day One.”

As the video closes, Walker affirms his tough stance:

“I refused to live with a deal that threatens our safety and that of our closest allies,” Walker says. “See, unlike others, I don’t need months or years to mull this over. If Congress fails to stop the nuclear deal, I will terminate it on day one. American leadership is back, and together with our allies, we will not surrender another inch of ground. America will not be intimidated, and neither will I.”