Former House speaker Newt Gingrich has dropped his bid for the 2012 Republican presidential nomination, but pledged to take up the role of "active citizen.''
"Today I am suspending the campaign. Suspending the campaign does not mean suspending citizenship,'' Gingrich said in a speech in the Washington suburb of Arlington, Virginia.
His withdrawal leaves only Ron Paul, a Texas congressman who represents the libertarian wing of the party, in the race against presumptive nominee Mitt Romney.
Gingrich had won just two nominating contests since the start of the state-by-state contest in January - in his home state Georgia and in South Carolina - and was a distant third in the fight to take on US President Barack Obama in November.
Former US senator Rick Santorum quit the race last month.
Paul consistently placed fourth in the primary season and has no chance of catching Romney, who has effectively launched his general election campaign against the Democratic incumbent.
Gingrich, who was often critical of Romney during the nomination race, said he was by far a preferable alternative to Obama, who is seeking a second term.
"As to the presidency, I am asked sometimes - is Mitt Romney conservative enough? My answer is simple - compared to Barack Obama?'' Gingrich said.
"This is not a choice between Mitt Romney and Ronald Reagan. This is a choice between Mitt Romney and the most radical, leftist president in American history.''