Still, as its most recognizable face, MSNBC has marshaled behind Mr. Olbermann, who on July 3, in an eight-minute “special comment” at the close of his show, addressed President Bush directly and called on him to resign. Two months later, the channel chose Mr. Olbermann to serve as the principal host of its coverage of a major prime-time address by Mr. Bush.

Mr. Olbermann’s “special comments” — more than 20 in the last 12 months, and nearly all of them first-person editorials that find some fault with the administration — have helped increase the ratings of his program by 33 percent in just the last year, to about 773,000 viewers a night, according to Nielsen. With those ratings, Mr. Olbermann’s program surpassed “Paula Zahn Now” on CNN, which was canceled last summer.

Image Rosie ODonnell, known for her liberal views, has been mentioned as a possible host for a talk show on MSNBC. Credit... Hiroyuki Ito for The New York Times

Mr. Olbermann comes on after “Hardball” with Mr. Matthews, whose longtime opposition to the war — and to what he describes as Vice President Dick Cheney’s outsize role in the administration — has become only more pointed since he took on the title of managing editor of his broadcast over the summer.

Since then, he has talked, both on the air and off, about the “criminality” of the Bush White House, as epitomized, he says, by the role of I. Lewis Libby Jr., the vice president’s former chief of staff, in the C.I.A. leak case. Mr. Matthews’s overall ratings have edged up in the process, though not on the scale of Mr. Olbermann’s.

Even Joe Scarborough, once a conservative congressman from Florida who stood behind President Bush during a campaign rally in 2004, has seemed to have a change of heart about his fellow Republicans in recent months, as is obvious to viewers of “Morning Joe,” his new morning show on MSNBC. In recent weeks, he could be heard praising Senator Hillary Rodham Clinton’s outreach to the military and her husband’s accomplishments as an ex-president, sentiments that, he acknowledged, had surprised even him.

In a telephone interview yesterday morning, hours before the news of the O’Donnell negotiations surfaced, Mr. Scarborough sounded more like Mr. Olbermann than vintage Newt Gingrich.