By all accounts, Keith Olbermann is quite the blowhard. A liberal version of Fox News host Bill O'Reilly - without Congress and the White House in his corner - he could have his own version of a Stephen Colbert imitator if only the American right had a sense of humour.

But his recent tirade against the Bush administration in general and defence secretary Donald Rumsfeld, who compared those who oppose the war in Iraq to appeasers before the second world war, was not just a tour de force but a real indication of how the centre of political gravity is shifting in the US concerning the conflict.

Rumsfeld was expounding what seems to be Bush's strategy for September to browbeat the American public back into line over the war. But as time goes on, the administration's opportunities to exploit the war for partisan ends appears to be fading. Olbermann, a presenter for cable channel MSNBC, basically compares these tactics with the legacy of Nixon, McCarthy, Neville Chamberlain and, at times, seems to implicitly compare them to Nazis themselves.

What feels remarkable about this is not that most Americans would agree with Olbermann's take on the Bush administration, but because just a couple of years ago this kind of talk would have been considered not just unpatriotic but heretical. People have been saying these things for quite some time, but rarely have such views received airtime in anything approaching the mainstream media.

Olbermann's ratings are low but growing rapidly (by more than 30% among the 25-54 age group in the last quarter). For with polls showing a solid and significant majority in favour of either immediate withdrawal or a timetable for it, the mainstream of the American public has been waiting a long time for the media to catch up. Finally that time seems to be arriving.