Mark is still clearly working for CBS News at the White House, but as a heavy CBS News radio top of the hour newscast listener...I'm wondering why he's never on the radio any more? Peter Maer, the other radio correspondent for CBS News Radio is on virtually all the time, was on the recent overseas trips,etc. Mark is frequently seen (and heard) at the daily press briefings which the cable news nets tend to carry, but has anyone heard why Mark is not on the radio...btw...Knoller is one of the most prolific twitterers there is...check out his twitter feed for a constant stream of White House news and inside...fascinating....