Keith Olbermann’s abrupt departure from MSNBC should be another wake-up call to American progressives about the fragile foothold that liberal-oriented fare now has for only a few hours on one corporate cable network.

Though Olbermann hosted MSNBC’s top-rated news show, ‘Countdown with Keith Olbermann,’ he disappeared from the network with only the briefest of good-byes. Certainly, the callous treatment of Olbermann by the MSNBC brass would never be replicated by Rupert Murdoch’s right-wing Fox News toward its media stars.

At Fox News, the likes of Bill O’Reilly, Glenn Beck and Sean Hannity have far greater leeway to pitch right-wing ideas and even to organize pro-Republican political events. Last November, Olbermann was suspended for two days for making donations to three Democratic candidates, including Arizona’s Rep. Gabrielle Giffords, who was wounded in the Jan. 8 shooting in Tucson.

Now, with Olbermann’s permanent departure on Friday, the remainder of MSNBC’s liberal evening line-up, which also includes Rachel Maddow, Ed Schultz and Lawrence O’Donnell (who will fill Olbermann’s 8 p.m. slot), must face the reality that any sustained friction with management could mean the bum’s rush for them, too.

The liberal hosts also must remember that MSNBC experimented with liberal-oriented programming only after all other programming […]