Rand Paul has decided to drop out of the White House race after a disappointing fifth place finish in the Iowa caucuses.
The Kentucky senator often clashed with his Republican rivals over their hawkish views on foreign policy and their support of government surveillance.
Rand Paul ended his bid in part to focus on his re-election to the Senate.
He is seen as representing the Libertarian wing of the party, which promotes individual rights and privacy.
“Across the country thousands upon thousands of people flocked to our message of limited government, privacy, criminal justice reform and a reasonable foreign policy,” he said.
“Although, today I will suspend my campaign for president, the fight is far from over.”
Rand Paul, an ophthalmologist, represents Kentucky in the Senate and is the son of former Congressman Ron Paul, who ran for president several times.
He has said in the past he is the right candidate to “stand up to both the right and the left”.
In 2015, a Time magazine cover labeled Rand Paul “the most interesting man in politics”.
There are now 10 Republicans left in the White House race, down from the original 17.
Rand Paul, 52, hoped to gain the attention of young people hoping for change but was ultimately overshadowed by billionaire businessman Donald Trump.
He is known for holding up the Senate floor for nearly 13 hours to delay the nomination of John Brennan as CIA director because of his opposition to the Obama administration’s use of drone strikes against terrorists.
He also was criticized last year when he said vaccines could give children “profound mental disorders”. He later said his children are immunized.
Rand Paul was passionate about criminal justice reform, saying the US needs to “break the cycle of incarceration for non-violent ex-offenders”.
He was praised for level-headed debate performances, but ultimately was hurt by his non-interventionist polices after terrorist attacks in San Bernardino, California and Paris.
Rand Paul had trouble raising money for his campaign, as well, not attracting wealthy donors flocking to candidates like Marco Rubio, Jeb Bush and Ted Cruz.
With such a large field of candidates, underperforming Republican candidates are under increasing pressure to drop out of the race.
Former Governor of Arkansas Mike Huckabee dropped out on February 2 as votes were being cast in Iowa.
Donald Trump is still leading the Republican race for the White House after causing further controversies in the first debate in Cleveland.
His refusal to rule out a third-party run drew boos from the audience on Thursday night.
Donald Trump stood by offensive comments he has made in the past about women.
The ten candidates in Cleveland, selected by Fox News on the basis of recent national polls, provided a frank and bruising exchange of views.
Facing some tough questions from the debate moderators, the candidates tried to stand out in a crowded Republican field.
Donald Trump stumbled on his past support for a national healthcare system but his most uncomfortable moment came when moderator Megyn Kelly challenged him on his views about women.
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“You’ve called women you don’t like fat pigs, dogs, slobs and disgusting animals,” Megyn Kelly said.
The tycoon answered by joking that he only said that about actress Rosie O’Donnell and stating that political correctness was one of the country’s biggest problems.
The crowd became hostile when Donald Trump said he would run as an independent, an admission that enraged Rand Paul.
“He buys and sells politicians of all stripes,” said the senator.
One of the loudest rounds of applause was for Marco Rubio when he mocked Hillary Clinton, who leads the Democratic field.
“First let me say, I think God has blessed us. He’s blessed the Republican Party with some very good candidates. The Democrats can’t even find one.”
On August 6, the Democratic Party announced it would hold its first debate in Nevada in October, hosted by CNN.
By next summer, each party will have a presidential nominee who will do battle in the race for the White House. Votes will finally be cast in November 2016.
The Republican field is one of the largest in recent years. Seven other candidates took part in an earlier debate that featured several attacks on Donald Trump.
Former Texas Governor Rick Perry said Donald Trump was running a campaign based on celebrity, while former Hewlett-Packard CEO Carly Fiorina mocked him over his Clinton ties.
While the debates were going on, Hillary Clinton was in Los Angeles for a campaign fundraising event attended by several celebrities, including reality TV star Kim Kardashian and her husband, Kanye West.