MSNBC anchor David Gregory may have been dancing up a storm with Chris Brown this morning on Today, but last week, his choreography wasn't so great.

That's because Gregory reportedly backstabbed a colleague in order to get on the NBC Nightly News, reporting on the Scott McClellan book scandal, all the while edging out NBC correspondent Kevin Corke, who did most of the reporting.

When news started trickling in about what McClellan would be saying in What Happened, Corke was traveling with President George Bush, who was in Colorado at the Air Force Academy. Producers had locked in Corke to report on the book's controversy for that evening's broadcast on May 28.

Except Gregory, who, we're told, hasn't appeared on Nightly News since he began his 6pm MSNBC show, made his case to anchor Brian Williams to let him lead the segment, since it was Gregory who was regularly covering McClellan two years ago, when he was White House press secretary.

"It was a classic 'big foot' [that] Gregory has long been known for," says a well-placed insider.

Except when Gregory stole the show this time, others began criticizing his move. After all, "no correspondent is better liked than Kevin Corke," says our source. He's "a consummate pro."

Not that Corke said anything about this to Williams or his superiors, we're told. Rather, it's the producers and crews that Corke works with, who were privy to Gregory's big footing, that are making a stink.

Says our insider: "Nobody will forgive Gregory for big footing a guy as well liked and hardworking as Corke. And the fact Gregory doesn't see this shows just how much Gregory's judgment is impaired."

And just to keep things interesting, remember that it was McClellan who, in his book proposal, promised an entire chapter of a hatchet job to taking down Gregory, but that chapter went missing in the final copy. Not that it stopped Gregory from lashing back at McClellan once the book did hit.