McCain's last standing rival drops White House bid

Long-shot White House hopeful Ron Paul formally abandoned his campaign for the Republican presidential nomination, vowing to remain on the political scene.

Paul, an anti-war libertarian, was the only contender to remain in the Republican race after Arizona Sen. John McCain clinched the party's presidential nomination in March.

As he ended his White House bid, Paul launched another campaign in a letter to supporters posted on his new Web site.

"With the primary season now over, the presidential campaign is at an end. But the larger campaign for freedom is just getting started," the nine-term Texas Congressman wrote, announcing the "Ron Paul Campaign for Liberty."

"We will be a permanent presence on the American political landscape. That I promise you," he said.

Paul, an obstetrician-gynecologist from the Houston area, said his new organization aims to be an alternative for libertarian-leaning Americans frustrated with the US political system.