Gov. Scott Walker drops out of GOP race

Chuck Todd and Kelly O'Donnell
Governor of Wisconsin Scott Walker.
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Wisconsin Gov. Scott Walker ended his White House bid on Monday and called on other Republican presidential candidates to do the same.

A source familiar with the decision tells NBC News that the decision to leave the race was made in the last 24 hours. Walker held a meeting with a small group of outside advisers at the governor's residence to discuss the move.

The governor had been presented with a number of options in terms of a political roadmap, mostly concentrated around an aggressive push in the key early state of Iowa. Faced with flagging campaign fundraising, Walker chose not to take that path, which would have required a major shakeup of his campaign infrastructure.

"It's been a rough couple of weeks and a decision needed to be made," said one person with knowledge of the conversations.

The Republican was once considered a frontrunner for the GOP nomination, topping polls in Iowa and winning accolades from conservatives for his fights against labor unions during his tenure as governor of the state.

But a series of missteps—and the rise of unconventional candidates like Donald Trump and Dr. Ben Carson—found him plummeting in national and key early state polls.

A CNN/ORC poll out this weekend found Walker winning support from less than one-half of one percent of GOP primary voters.

Walker's performance was lackluster in the two GOP primary debates to date, and he had faced calls to shake up his campaign staff.

He had also been lambasted for unclear answers and flip-flops, particularly involving his views on immigration policy.

He is the second Republican candidate to exit the presidential race. Texas Gov. Rick Perry dropped out before last week's CNN debate in Simi Valley, California.

Walker's network of endorsers and campaign staff will now be in high demand.

At an event held Monday night by the National Review and Google, Marco Rubio's campaign manager said that the Florida senator has already secured the support of Walker's New Hampshire state co-chair.