Bob Barr is Libertarian candidate for president

(CNN) - Former Georgia Congressman Bob Barr was nominated officially Sunday as the Libertarian candidate for president.

Barr, who played a prominent role in the impeachment of former President Bill Clinton, told supporters at the Libertarian National Convention in Denver, "We have only 163 days to win this election."

Some GOP observers are watching to see if Barr will draw votes away from the presumptive Republican nominee, Sen. John McCain of Arizona, in the general election.

Barr, 59, left the Republican Party in 2006. He was elected to the House of Representatives in 1994 and represented a conservative district in the Atlanta suburbs for four terms. In his last term, Barr became an increasingly vocal critic of President Bush.