They came, they campaigned, they exited: 2012 GOP presidential contenders

Throughout the primary numerous Republican hopefuls fought for their party's nomination. One-by-one the candidates withdrew as low poll numbers, weak election results and political gaffes brought their campaigns to a halt. 

Newt Gingrich, a one-time frontrunner, was the most recent campaign trail casualty. The former House Speaker officially withdrew his candidacy Wednesday, after a series of Northeastern primary loses in mid-April that led to continued speculation about the viability of his campaign. 

"I'm suspending the campaign. But spending the campaign does not mean suspending citizenship," Gingrich said at a speech to supporters in Arlington, Va. 

Former Minnesota Gov. Tim Pawlenty was the first major Republican candidate to drop out of the race, following a disappointing finish in the Ames Straw Poll in Iowa. 

"I wish it would have been different, but obviously, the pathway forward for me doesn't really exist, so I'm going to be ending my campaign," said Pawlenty in interview with ABC's "This Week" in August. 

In between, Herman Cain, Rep. Michele Bachmann (Minn.), former Utah Gov. Jon Huntsman, Texas Gov. Rick Perry and former Sen. Rick Santorum (Penn.) all ended their bids for the presidency, leaving Romney, the former Massachusetts governor, and Rep. Ron Paul (Texas) in the race.

Santorum mounted the most serious challenge to Romney. But trailing in the delegate count, he withdrew before suffering a defeat in his home state of Pennsylvania.

Paul has remained in the race, despite his diminishing relevance in the contest and a low delegate count. 

Bachmann, who ended her campaign in January after disappointing results in Iowa, formally endorsed Romney Thursday at a campaign stop in Portsmouth, Va. 

With Romney all but guaranteed the Republican nomination, he and President Obama are primed to face off in an extremely tight race heading into November's election.