Asking Republican presidential candidates whether they would have invaded Iraq, “knowing what we know now,” paid an immediate dividend, insofar as it helped cement historical judgment against the war. But if that’s the end of the line of inquiry, the question has the power to do real damage beyond airy issues of collective memory.

Several writers have made similar points in different ways, James Fallows and Peter Beinart of The Atlantic most effectively: If today’s Republicans can avoid grappling with the Iraq war beyond admitting that it looks like a mistake in retrospect, they can gloss over the extent to which it represented an error in judgment on its own terms and was moreover thrust upon the world, rather than blundered into on the basis of faulty intelligence alone.

To allow these candidates to say, “in hindsight, we shouldn’t have invaded,” and leave it at that is to pull back the rug and open the escape hatch for them. Perhaps some of them regret having invested in Lehman Brothers, too, and yet no reporter would allow that to suffice as a reckoning with decades of financial deregulation leading up to the economic crisis.

But the imperative to dig deeper is greater than to simply prevent people who supported the war until two weeks ago from evading questions about their judgment, and glossing over the ugly historical truth. These Republicans—with the possible exception of Jeb Bush—are thrilled to say they wouldn't have invaded Iraq, not because they take great pleasure in throwing the last GOP president under the bus, but because it will allow them, first in the primary and then in the general election, to attempt the greatest volte-face in the recent history of presidential politics. Having washed their hands of the war and escaped further interrogation about it, they can turn around and attack Hillary Clinton over the Iraq war from the left.

Jeb Bush was the obvious mark for all these Republican mea sorta culpas. His inability to articulate a coherent answer to a predictable and easy question invited the rest of the GOP field to chime in and appear forthright by comparison. But they have a different target in mind as well.