A conservative group is airing an ad showing kids counting down to a mushroom cloud to slam Democratic Sen. Michael Bennet of Colorado over the Iran nuclear deal.

The ad by the group Advancing Colorado shows children counting down from 10 in different languages, then a huge explosion and billowing cloud. Over charred and smoking rubble it claims that Bennet is “jeopardizing our safety” by backing the deal.

The ad offers a taste of how the GOP may seek to use the Iran issue politically after Senate Democrats including Bennet blocked Republican attempts to unravel the deal. Bennet is up for re-election next year in a competitive state, though Republicans don’t yet have a candidate against him. He is the most vulnerable Senate Democrat this cycle, but in 2018 a number of potentially vulnerable Democrats will be defending their seats and Republicans will likely try to make them pay a price for supporting the agreement.

The accord backed by the Obama administration and negotiated with Iran and five world powers aims to curb Iran’s nuclear program in exchange for billions in relief from economic sanctions. But Republicans say it will serve only to empower Iran.

The incendiary ad is reminiscent of the famous “Daisy ad” that President Lyndon Johnson used against Republican opponent Barry Goldwater in 1964. Johnson’s ad showed a little girl picking daisy petals, then a billowing mushroom cloud. Johnson was trying to portray Goldwater as a warmonger over Vietnam.

Jonathan Lockwood, executive director of Advancing California, said the in-your-face approach was appropriate to tell voters about Bennet’s role in a dangerous agreement. “The consequences of this deal are going to be even more shocking than this ad,” said Lockwood.

But a spokesman for Colorado Democrats called the ad a “smear” and said Bennet is working to improve the Iran deal and has sought to make Coloradans safer.

“With Washington Republicans lacking an opponent in the Colorado Senate race, it comes as no surprise that a secretly funded group with ties to the billionaire Koch brothers is out with a deeply offensive, fear-mongering attack against Sen. Bennet,” said Andrew Zucker, senior communications adviser at the Colorado Democratic Party.

Lockwood, who formerly ran the conservative billionaire Koch brothers’ Colorado young voter outreach organization, said Advancing Colorado is not funded by the Koch brothers, though he declined to disclose donors. He said the ad buy was six figures, including broadcast stations in Denver starting Tuesday, and online and digital. Democrats said the broadcast portion is only $46,000, which Lockwood didn’t dispute, making it a fairly small buy.

(AP)