If you're wondering why Ron Paul is sometimes called an isolationist on foreign policy, his role in Thursday night's Republican debate sheds some light.

The congressman from Texas won some loud applause, but also walked out on a precarious limb with many conservative voters, for picking a fight with fellow Republican candidates on US military policy.

The issue was Iran.

Here's a look at who said what, and the sharp divide over foreign policy and national defense that it illuminated. The chasm was so wide that it left some political analysts saying Mr. Paul sounded crazy. ("Jumped the shark" was the specific phrase used by an analyst with the Fox News network, which hosted the debate.)

For his part, Paul was arguing that other Republicans are essentially pursuing a crazy policy. "Absurd" and "dangerous" were words he used. He also, on the day US military operations officially ended in Iraq, called the war launched there in 2003 by the US and its allies "useless."

Paul and his rivals for the Republican presidential nomination clashed over the seriousness of the threat from Iran, what Iran's geopolitical objectives are, and what US policy should be.

Moderator Bret Baier started the discussion with a question directed at Paul: What would he do, as president, if presented with intelligence showing that Iran had a nuclear weapon? And, by opposing economic sanctions against Iran, is he running to the left of President Obama?

Ron Paul: "You know what I really fear? ... It's another Iraq coming. It's war propaganda going on," he said. "To me, the greatest danger is that we will have a president that will overreact."

He likened the current situation to views of Iraq in 2003: an atomosphere of alarm without solid evidence on the question of weapons capability. "If we lived through cold war, which we did, with 30,000 missiles pointed at us, we ought to really sit back and think, and not jump the gun.... That’s how we got involved in the useless war in Iraq and lost so much."

Similar to his position on Iraq back then, he voiced skepticism that Iran is close to obtaining a nuclear weapon. Paul said it's also important for US policymakers to keep the regional context in mind: Iran feels surrounded by other nations that have nuclear arms, and has seen evidence that nuclear nations get some respect.

Regarding sanctions, he called them an "act of war" that could damage the European economy by diminishing the flow of oil.

Rick Santorum: The former senator from Pennsylvania got a chance to respond to Paul's view, and hit back hard. Iran has essentially been "at war with us since 1979," he argued, citing Iran as a factory for the IED bombs that killed many US soldiers in Iraq.

"They are a radical theocracy," Mr. Santorum said. "Mutual assured destruction, like the policy during the cold war with the Soviet Union," wouldn't work on Iran because "their principal virtue is martyrdom.... They believe that it is their mission to take on the West."

He called for covert actions leading toward potential strikes, so the US can "say to them that if you do not open up those facilities and close them down, we will close them down for you."

Mitt Romney: The former Massachusetts governor criticized Mr. Obama for being timid by asking for a US drone back after it fell into Iranian hands. "A foreign policy based on pretty please? You’ve gotta be kidding?" he said. Mr. Romney called for new buildup of the Navy fleet and for adding 100,000 soldiers to US ranks, saying a strong America must lead the free world.

Michele Bachmann: The congresswoman from Minnesota seized an opportunity to fire her own shot at Paul. "I think I have never heard a more dangerous answer for American security than the one we just heard from Ron Paul.... And the reason why I would say that is because we know without a shadow of a doubt Iran will take a nuclear weapon, they will use it to wipe our ally Israel off the face of the map. And they've stated that they will use it against the United States of America."

She added, "Look no further than the Iranian constitution, which states unequivocally that their mission is to extend jihad across the world and eventually to set up a worldwide caliphate. We would be fools and knaves to ignore their purpose and their plan."

Paul: He offered a different take on the objectives of the Iranian regime and of the world's adherents of Islam in general. "To declare war on 1.2 billion Muslims and say all Muslims are the same, this is dangerous talk. Yeah, there are some radicals. But they don't come here to kill us because we're free and prosperous. Do they go to Switzerland and Sweden? I mean, that's absurd. If you think that is the reason, we have no chance of winning this. They come here and they explicitly explain it to us. The CIA has explained it to us. They said they come here and want to do us harm because we're bombing them."

He espoused a view of limited war powers for the executive branch, and of economic limits to American military engagement. "Why do we have to bomb so many countries? Why are we [having] 900 bases in 130 countries and we're totally bankrupt? How are you going to rebuild the military when we have no money?... We need a strong national defense ... and we need to only go to war with a declaration of war."

Bachmann: She took a rebuttal opportunity. Where Paul had talked about the danger of overreacting on Iran, she said it "would be that the greatest underreaction in world history if we have an avowed madman who uses that nuclear weapon to wipe nations off the face of the Earth and we have an IAEA [International Atomic Energy Agency] report that recently came out that said literally, Iran is within just months from being able to obtain that weapon."

Paul: He responded, saying the IAEA report did not contain hard evidence of an imminent nuclear weapon. Paul was booed, while later a CNN "truth squad" said Paul was factually correct on this point.

Because of the way the debate was structured, presidential contenders Newt Gingrich, Jon Huntsman Jr., and Rick Perry did not have an opportunity to weigh in on Iran. Mr. Gingrich has said he favors "regime change" in Iran, and that, if elected president, he could topple Iran's government within a year, but would use military force only as a last resort.

Mr. Huntsman has said the US and Israel will have to consider the military option to prevent Iran from developing a nuclear weapon, because economic sanctions won't be enough.

Governor Perry proposes to take "every economic and diplomatic effort" to stop Iran, and would have the military option "on the table." He lambasts Obama's Iran policy, but it's not clear how his would differ.