President Bush has kept Air Force One pretty busy in his six years, but Washington's pre-eminent expert on presidential travel says that at his current foreign travel rate, Bush won't best his predecessor. "He's creeping up on Clinton's record," says CBS Radio's White House correspondent Mark Knoller, whose records on presidential travel even the White House refers to as the authoritative source. So far, Bush has done 36 overseas trips to 58 countries, an average of six a year. Clinton completed 55 to 72 countries. W did beat his dad: In four years he made just 23 trips to 36 nations.