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Wisconsin Gov. Scott Walker suspended his presidential campaign Monday and encouraged other Republican candidates to abandon their White House bids so that voters can focus on “a positive, conservative alternative to the current frontrunner.”

“Today I believe that I am being called to lead by helping to clear the field in this race so that a positive, conservative message can rise to the top of the field,” Walker said in a statement to reporters in Madison, Wisconsin.

“With this in mind, I will suspend my campaign immediately,” he said. “I would encourage other Republican presidential candidates to do the same, so that the voters can focus on a limited number of candidates who can offer a positive, conservative alternative to the current frontrunner.”

It was a not so subtle dig at GOP frontrunner Donald Trump, who continued to maintain his lead in the polls after the second Republican debate. Trump has taken aim at many of his rivals, including Walker, with attacks that many times turn personal.

“Sadly, the debate taking place in the Republican party today is not focused on that optimistic view of America. Instead, it has drifted into personal attacks,” Walker said.

Before Walker delivered his statement, Trump tweeted praise for his former rival.

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I got to know @ScottWalker well—he’s a very nice person and has a great future. — Donald J. Trump (@realDonaldTrump) September 21, 2015

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.