At least several thousand people marched this weekend on the Pentagon, roughly between 5,000-8,000 would be a good guess - since the Park Service doesn't do official counts anymore. It was substantially smaller than than many of the protests I've covered in previous years - 2003 in DC and the 2004 Republican National Convention in NYC - but I was surprised that there was even this much of a turnout - mostly young folks, with a few noticeably visible vets up front. Protests in the U.S., both anti-war and anti-globalization, seem to have fallen off dramatically in the last few years.
