Rep. Ron Paul, R-Texas, has earned the nickname "Dr. No." for voting against anything that hasn't been explicitly authorized by the Constitution. In 1988, he ran for president as a Libertarian. Today, Paul is the only GOP contender who wants to withdraw U.S. troops immediately from Iraq. While Paul, 72, is considered a longshot for the White House, his supporters have helped him set a new fundraising record in December 2007 for the most money raised in a single day via the Internet (slightly more than $6 million).