The emergence of John Bolton as a potentially critical witness in Democrats’ case for ousting President Donald Trump from office is deeply ironic.

For years, Democrats almost to a person have depicted the former national security adviser and arch-conservative as practically unhinged. Now, by contrast, Democrats consider him a solid and stable foundation upon which to rest their case for the president’s conviction in his ongoing impeachment trial.

Republicans have flipped, too, on Bolton — and might flip in greater numbers in the coming days. Bolton has long been hailed in GOP circles as the virtual apotheosis of clear-eyed, credible conservatism on foreign policy, the voice of a worldview grounded in a strong sense of right and wrong and a detail-oriented approach that was supposed to bring discipline to the National Security Council.

Then came Sunday’s revelation that Bolton will say in a forthcoming book that the president himself had acknowledged hinging military aid to Ukraine in 2019 on Kyiv’s announcement of unfounded investigations that could cast certain Democrats in a bad light.