Ron Paul and Rand Paul agree on a lot, but they don’t agree on what the U.S. should do about the Islamic State group in Iraq and Syria.

Ron Paul, the former Republican congressman from Texas, tells U.S. News he would “definitely not” vote to give President Barack Obama authority to wage war against the jihadi militants.

Fighting the group, he says, "will just hurt us and it will end when we go bankrupt.”

Rand Paul, the Kentucky senator and possible 2016 Republican presidential candidate, held a non-interventionist stance for much of the Syrian Civil War, but told Fox News Monday he would vote to bless Obama's use of force after the group beheaded two American journalists.

Obama claims he doesn't need - but would welcome - congressional approval to launch air strikes.

The senator’s position is full of caveats. He doesn’t want an open-ended authorization of force and opposes Obama's plans for arming the so-called moderate Syrian opposition.

But, Rand Paul made clear in a Sept. 4 editorial for Time, “I support destroying the Islamic State in Iraq and Greater Syria (ISIS) militarily."

His father, famously firm in his non-interventionist beliefs, doesn’t.

“If we weren't there nobody would be getting killed,” Ron Paul says. “If ISIS still existed without us being there, maybe [Syrian President Bashar] Assad and maybe Iran would take care of them.”

Editorial Cartoons on the Islamic State View All 82 Images

"They hate each other and we hate ‘em all - except for the Free Syrian Army, those moderates who made $50,000 handing over the journalist to ISIS - if that isn't an insane foreign policy I don't know what the definition of insanity is," he says, referring to reports that U.S.-backed rebels helped jihadis capture journalist Steven Sotloff, who was recently beheaded.

The retired congressman, who sought the GOP presidential nomination in 2008 and 2012 and ran for president as the Libertarian Party’s candidate in 1988, says there’s a simple explanation for the different positions.