US Republican Rand Paul has suspended his 2016 presidential bid after his small-government campaign failed to gain traction with voters.
The US senator from Kentucky on Wednesday (local time) became the second Republican candidate, behind former Arkansas Governor Mike Huckabee, to drop out of the race since Monday's night's Iowa caucuses.
That contest launched the parties' process to nominate candidates for the November election.
"It's been an incredible honour to run a principled campaign for the White House. Today, I will end where I began, ready and willing to fight for the cause of Liberty," Paul said in a statement.
In the Republican race, the libertarian-leaning Paul finished in fifth place in Iowa with 4.5 percent of the vote, struggling to attract support in a crowded field.
US Senator Ted Cruz finished first in Iowa, putting a dent in real estate tycoon Donald Trump's standing as front-runner to be his party's nominee.
Paul, who is also focused on winning another US Senate term, said he would continue fighting for limited government, criminal justice reform and "reasonable" foreign policy.
His withdrawal leaves 10 Republican candidates in the 2016 White House race.