How Scott Walker's Presidential Candidacy Crumbled

— -- Scott Walker is now officially out, announcing at a press conference Monday that he was withdrawing from the presidential contest so that a “positive conservative message can rise to the top of the field” and buttress the current frontrunner, Donald Trump.

Amounting to one of the shortest presidential campaigns in modern history –- lasting just 71 days -– Walker had seen his polling numbers crater in recent months compared to the time ahead of his entry into the field, when he was widely viewed as one of the most promising contenders.

Running as a Washington outsider and heralded for his success in pushing through conservative reforms in the politically purple state of Wisconsin, Walker’s campaign began to lose steam almost as soon as it was launched.

So what happened?

After polling as the frontrunner in the first-in-the-nation caucus state of Iowa for the better part of the year, Walker’s numbers began to slip in Iowa and nationally as Trump surged to the top of the field. In the most recent national poll, released by CNN/ORC over the weekend, Walker registered just 0.5 percent. And in Iowa, Walker slid from 19 percent to 5 percent in just six weeks of NBC News/Marist polling.

In addition to Trump’s climb, Walker’s fall was abetted by his own lackluster performance in the first debate and a series of missteps in articulating his position on immigration reform and at one time suggesting that he considered building a wall with Canada to be a “legitimate idea.”

But Walker’s hasty exit from the Republican nominating contest was about more than just sagging poll numbers and sloppy statements. It was about money, sources told ABC News.

Walker's campaign did not file its financials with the Federal Election Commission because of the short time it was in existence.

The size and scope of Walker’s campaign, which was reportedly comprised of some 90 paid staff, had been built for a frontrunner. And when Walker failed to perform as such, the fundraising simply couldn’t keep up with the operation.

Reed Galen, a Republican political consultant who served as John McCain deputy campaign manager until July 2007, points out that the campaign never had the benefit of frontrunner status while Walker was actually in the race, since Walker’s strongest stretch in the polls – particularly in Iowa – came before he was a declared candidate.

“The campaign did not exist with the benefit of being a frontrunner,” Galeen said. “And so now you're in a place where you thought you would be in first place … you get a heightened sense of your success based on 42 minutes at a podium, then a lackluster performance at the first debate, he’s had a number of issue on immigration and birthright citizenship, and all these things aggregate together in a noxious mix.”

And while Walker did have a Super PAC raising money for him during that time, Super PACs alone cannot support campaigns.

“Regardless of how much Super PAC money you have behind you, these candidates have to take a good hard look at their prospects and say I could keep doing this, but let’s be realistic and wake up on Tuesday morning, am I going to be in a better place?” Galeen said. “Do I have the time to get to the next debate, which is the next opportunity for me to make a splash.”

A few days ago, Walker had reshuffled his campaign calendar to refocus his efforts on Iowa and South Carolina, two states where his message had shown early promise among the conservative Evangelical base of voters. But even with a focus on those states, Walker’s campaign was facing organizational woes.