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.
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.