Ben Carson ends his campaign for the Republican presidential nomination

After hinting earlier in the week about his likely exit from the presidential race, retired neurosurgeon Ben Carson made it official Friday, telling a major gathering for political conservatives outside Washington that he is leaving the campaign trail.

Carson, who perched briefly near the top of the polls last fall thanks to voters drawn to his Christian faith and status as an outsider, failed to win any early nominating contests and battled staff shake-ups within his campaign. He sat out Thursday night's debate, a day after saying he did not see how he could win the GOP nomination.

In the 10 months Carson traversed the country vying for the nomination, he did manage to rake in large sums of cash, but burned through the money almost as quickly as it was raised.

Dismal debate performances in which Carson showed difficulty grasping foreign and domestic policy issues also doomed his candidacy.

His departure narrows the field of contenders to four, including front-runner Donald Trump, whose brash and blunt rhetoric has appealed to a segment of Republicans in early nominating states.

Trump now claims the title as the lone political outsider in the field, running alongside Sens. Ted Cruz of Texas and Marco Rubio of Florida and Ohio Gov. John Kasich.

Cruz has persistently called on others to exit the race, noting that he's the candidate who has beaten Trump the most. And as the primary heads to winner-take-all contests in Ohio and Florida on March 15, Kasich and Rubio are faced with must-wins in their home states. A loss to Trump would seriously impair their candidacies.

'This idea of the field clearing and Republicans rallying around a single candidate to take on Trump isn't going to happen,” said Stuart Stevens, a senior adviser in 2012 to Mitt Romney. '(Trump's) on the way to the nomination. These guys should have taken him on months ago and failed to do so.”

It was three years ago when Carson, who is retired from his position as director of pediatric neurosurgery at Johns Hopkins Hospital, entered the political world.

At the National Prayer Breakfast that year, Carson gained plaudits from conservatives for castigating President Barack Obama's health care law while the president sat nearby.

But Carson's comments since, including calling Obamacare the 'worst thing that has happened in this nation since slavery,” drew criticism from Democrats and Republicans.