The Hillary Clinton campaign on Thursday continued its pushback against Bernie Sanders’ stance on Iran and the war against ISIS as an issue for concern in the Democratic presidential primary.

In a conference call with reporters on Thursday, former State Department official and now senior policy advisor to Hillary, Jake Sullivan argued that Sanders’ proposal to more aggressively normalize relations with Iran “not only breaks with President Obama’s policy, it breaks with the sober and responsible diplomatic approach that’s been working for the United States.”

“That is like asking the arsonist to be the firefighter,” he asserted.

During the Democratic presidential TV debate in Charleston, South Carolina on Sunday evening, Sanders expressed his desire to see the U.S. move “as aggressively as we can to normalize relations with Iran.” According to the Jewish Senator from Vermont, after the administration has managed to reach a nuclear agreement with the Iranian regime without going to war, “the goal has got to be, as we have done with Cuba, to move in warm relations with a very powerful and important country in this world.” Hillary Clinton countered his position, highlighting Iran’s bad behavior on non-nuclear activity and its sponsor of terrorism in the region.

On Tuesday, 10 former senior U.S. diplomats and national security officials who have served across multiple administrations issued a joint statement raising questions about Sanders. “Over the past four debates, the subject of ISIS and Iran have come up a number of times,” they said in the statement distributed by the Clinton campaign. “These are complex and challenging times, and we need a Commander in Chief who knows how to protect America and our allies and advance our interests and values around the world. The stakes are high. And we are concerned that Senator Sanders has not thought through these crucial national security issues that can have profound consequences for our security.”

The emphasis on Sanders’ positions on national security come as new polls show the Vermont Senator opening a lead in Iowa and New Hampshire. A CNN poll published on Thursday showed Sanders with the support of 51% of likely Iowa democratic caucus-goers to Clinton’s 43 percent.

Recent public opinion polls also show Sanders leading potential Republican candidates by a larger margin than Hillary’s matchups.

But according to Brian Fallon, Clinton’s national press secretary, Sanders’ foreign policy positions would make him more vulnerable in the general election. “I can safely predict that Republicans would love to have a debate with someone who thinks we should move quickly to warmer relations with a major sponsor of terrorism like Iran,” said Fallon. “Bernie Sanders represents that caricature that Republicans like to put forward.”

The campaign also released a video on Thursday featuring Sullivan explaining the fundamental misunderstandings that Sanders’ proposals show and the inherent dangers they would pose. “Secretary Clinton supports diplomacy with Iran. But normal relations with Iran right now? President Obama doesn’t support that idea, Secretary Clinton doesn’t support that idea, and it’s not at all clear why Sen. Sanders is suggesting it.”