WASHINGTON — In a striking shift from President Donald Trump’s claims of “perfect” dealings with Ukraine, his defenders asserted Wednesday at his Senate trial that a trade of U.S. military aid for political favors — even if proven — could not be grounds for his impeachment.

Trump’s defense spotlighted retired professor Alan Dershowitz, a member of their team who said that every politician conflates his own interest with the public interest. Therefore, he declared, “it cannot be impeachable.”

The Republicans are still hoping  to wind up the impeachment trial with a rapid acquittal. Democrats are pressing hard for the Senate to call additional witnesses, especially Trump’s former national security adviser John Bolton. Bolton’s forthcoming book contends he personally heard Trump say he wanted military aid withheld from Ukraine until it agreed to investigate Joe Biden and his son, Hunter Biden — the abuse of power charge that is the first article of impeachment.

As Chief Justice John Roberts fielded queries in an unusual question-and-answer session, Texas Republican Ted Cruz asked, Does it matter if there was a quid pro quo?

Simply, no, declared Dershowitz, who said that many politicians equate their reelection with the public good.

“That’s why it’s so dangerous to try to psychoanalyze a president,” he said.