Last Thursday, we asked how long it would take before Lanny Davis again changed his story about what his client, Michael Cohen, knows about President Trump. It turned out to be four days.

Meanwhile, CNN is standing by a story that relied in part on claims that Davis now says he never should’ve made.

It all started with last month’s bombshell CNN report that Cohen, Trump’s former personal attorney, was claiming his then-boss knew in advance of the 2016 Trump Tower meeting between campaign officials and a Russian operative.

The CNN story said outright that Davis had declined comment, implying that he wasn’t a source — even though Davis now says he was, and CNN admits it. That same night, Davis confirmed the story anonymously to this newspaper and to The Washington Post.

Last week, however, Davis publicly stated that Cohen knew no such thing, and had never said otherwise. He then ’fessed up to his anonymous claims to the New York and Washington papers, while still insisting he wasn’t a source for the CNN report.

It was only this week that he admitted he actually was a CNN source. His excuse to Buzzfeed: He “made a mistake” and “unintentionally misspoke.” (Three times?)

CNN is standing by the story because it says it has at least one other source for it, and because it suspects Davis changed his story only because Cohen could face perjury charges, since he testified under oath to a Senate committee that he had no advance knowledge of the Trump Tower sitdown.

The network offers no justification for its own deception of reporting that Davis hadn’t commented when he actually had, though anonymously.

Davis, meanwhile, has also retracted at least two other claims about what Cohen “knows” about Trump. Maybe all those years as a Clinton spokesman just leave him unable to tell the truth, but what’s CNN’s excuse?