One of Jeb Bush's principal foreign policy campaign advisers, a man named Otto Reich who is a veteran of the Reagan and George W. Bush administrations, has just made a very odd and enthusiastic argument in support of the 2003 US-led invasion of Iraq, in which he repeats one of the most widely discredited justifications for the war.

The quote appears in the current issue of the New Yorker, in a piece by Ryan Lizza on Jeb Bush's struggles with foreign policy. It is quite jarring to read:

"I can defend the invasion of Iraq," Reich told me. "What did the invasion of Iraq do? It caused all of the people who would’ve otherwise come and attacked us and killed Americans on our soil — it caused them to go to Iraq and die there. That may sound very brutal, or whatever, but we have seen what has happened when you have an administration like the current one, that did not realize what Bush had done; sent the troops home from Iraq; created a vacuum that was filled by ISIS. And they’re killing Americans and everyone else — they’re mostly killing Muslims. I lay that at the feet of the Obama Administration."

Reich is repeating an idea, now largely rejected, that post-invasion Iraq served as "flypaper" for America's enemies, allowing us to fight them so they couldn't threaten us at home. President George W. Bush and other American officials used it as a kind of retrospective justification for the Iraq War after the WMD rationale fell apart.

Rick Santorum memorably endorsed it with a super-weird Lord of the Rings analogy: "As the hobbits are going up Mount Doom, the Eye of Mordor is being drawn somewhere else. It’s being drawn to Iraq and it’s not being drawn to the U.S. You know what? I want to keep it on Iraq. I don’t want the Eye to come back here to the United States."

But it's a very troubled argument. Best case, it boils down to saying the death of about 150,000 Iraqi civilians was worth it to kill some terrorists. But the basic idea — that Iraq weakened rather than strengthened the jihadist movement — was really, really hard to defend at the time, given that al-Qaeda used Iraq's post-invasion chaos as a base of operations and recruiting center. It's even harder to defend now with the rise of ISIS.

The Iraq War did not, research suggests, attract huge numbers of international terrorists who otherwise would have been plotting attacks on the US. It did, however, radicalize a lot of Iraqis. The group we now know as ISIS grew strong after the invasion by recruiting off anti-Americanism and the country's descent into sectarian civil war.

Many of the people who now lead ISIS met and built ties in American prison camps during the war. "If there was no American prison in Iraq, there would be no [ISIS] now," one ISIS leader told the Guardian's Martin Chulov.

The rise of ISIS, despite what Reich says, couldn't have been prevented by leaving a few more US ground troops in Iraq after the war ended. ISIS's growth was driven by the Syrian civil war and domestic Iraqi political divisions, problems that couldn't really be solved by American force. Moreover, the withdrawal of US troops was mandated by a 2008 US-Iraq Status of Forces Agreement negotiated by ... George W. Bush.

The fact that a top adviser to one of the most serious Republican candidates for president is making such a weak argument illustrates just how flimsy the case for the Iraq war has become, and how much trouble the issue could give Jeb Bush if he wins the nomination — given his last name.