The HuffPo founded guest-hosted Rachel Maddow's program Monday night. It's of note because for months MSNBC, whose primetime programs had been embracing progressive topics, refused to have Huffington on the air because, apparently, of a long-running feud that began when the late Tim Russert oversaw NBC News.

We wrote about this in detail back in May:

Progressive author and Internet powerhouse Arianna Huffington has appeared on MSNBC more than 30 times over the last 12 months, offering up her combative opinions on current events. The tally probably would have been double that if the stretched-too-thin writer and editor had accepted all the channel's requests that flood her office.

So when Huffington set out late last month to promote her new book, MSNBC seemed like an obvious first stop. In fact, producers had already been in touch, asking about Huffington's availability during her book push. And I hear an informal memo circulated within MSNBC detailing the order in which Huffington would appear on the various MSNBC news programs in coming weeks.

But then suddenly, the doors were slammed shut and Huffington's camp was told thanks, but no thanks; it was an across-the-board shutout from both MSNBC and its big brother, NBC.

Why the cold shoulder? In her latest book, which came out last spring, Huffington took aim at Russert, portraying him as a hapless, “conventional wisdom zombie.”