Former Republican Rep. Bob Barr is expected to announce that he's running for president as a Libertarian.

His candidacy would be a wild card in the White House race that many believe would hurt Republican Sen. John McCain.

Barr had scheduled a news conference Monday. He first must win the Libertarian nomination at the party's national convention that begins May 22. Party officials consider him a front-runner thanks to the national profile he developed as a Georgia congressman from 1995 to 2003.

Barr, 59, helped lead Bill Clinton's impeachment. He quit the Republican Party two years ago, saying he had grown disillusioned with its failure to shrink government and its willingness to scale back civil liberties in fighting terrorism.