Of all the curiosities of the 2016 Republican presidential race — and there have been plenty — the quietest may also be the most difficult to answer. Over the last two months, Wisconsin Gov. Scott Walker has gone from leading the field to barely making the debate cut.

The most recent Monmouth University poll of likely Iowa caucus-goers shows Walker in deep trouble. In July, the Wisconsin governor dominated the field, scoring 22 percent over Donald Trump's 13 percent, with Ben Carson in third place at 8 percent. Other current and former governors in the race didn't even get to a third of Walker's support; Jeb Bush scored 7 percent (tied with Sen. Ted Cruz), Mike Huckabee got 6 percent, and Bobby Jindal was the second-highest sitting governor in the race at 4 percent. Walker appeared ready to take control of the key Iowa caucuses and put his prairie conservatism at the center of the GOP's appeal.

Instead, just a month later, Walker has disappeared into the ranks of the also-rans. Trump and Carson now tie at 23 percent, and Carly Fiorina has moved up to third place with 10 percent. None of these three have ever won public office before, and yet 56 percent of Monmouth University respondents chose them over the deep Republican bench of 2016. The most dramatic reversal in the poll was Walker's, whose support plummeted from 22 percent to 7 percent. Combined, the entire GOP bench of currently elected officials only garnered 29 percent — barely more than half of the majority siding with that trio of newcomers.

This is not an isolated phenomenon for Walker. In the spring and into early summer, his national polling average at Real Clear Politics put him in the mid-teens. After peaking at 17.3 percent in April — when Walker led the field — the Wisconsin governor who fought the unions and won has bled out quickly. Other than a brief spike in July, it's been all downhill, culminating in this week's brutal 6.7 percent rating, only good enough for a distant fifth place behind Trump, Carson, Bush, and Cruz. In the Hot Air-Townhall Media Group national online poll, Walker barely registered, only getting 1.3 percent of 469 Republican respondents.

Walker's performance woes are not entirely due to outside factors. He has stumbled repeatedly on policy, offering confusing and at times contradictory statements. Walker seemed initially skeptical of ethanol price supports, but shifted his rhetoric later. On immigration, Walker has been all over the map, seemingly trying to shift with the party on issues like birthright citizenship, where other Republican candidates have also struggled. A lackluster debate performance on Fox, combined with the distraction of the feud between Trump and Megyn Kelly, may have precipitated the most recent part of Walker's fade.

However, at least Walker had a peak. The other GOP bench candidates who hold elected office — Chris Christie, Bobby Jindal, Rand Paul, and Marco Rubio — have not even enjoyed that measure of success. Still, Walker's case is even more curious than the rest, given the natural advantages he enjoyed even in a populist environment like 2016.

Want an outsider? Walker has never worked in Washington. Before winning the gubernatorial election in 2010, Walker was the Milwaukee County executive for more than eight years, and served nine years in the state legislature before that. His Senate rivals may have to dance around their brief time in Washington, and Bobby Jindal's House career might be a slight negative in an anti-establishment era, but Walker has no such baggage.

Want a fighter? Walker fought and beat the public-employee unions in Wisconsin, and then fought and beat them again in a recall election and a second gubernatorial bid. That's three election victories in four years. He drew heat from around the country on that fight and never backed down, and then added wins on other conservative agenda items such as Right to Work and voter ID laws.

Want a departure from the elite to the hoi polloi? Walker is custom made for the role. He shops at Kohl's, had never earned six figures until becoming governor, and has amassed little wealth in 48 years. He is the antithesis of Mitt Romney — a man of modest means and modest background who went into politics to serve rather than enrich himself.

In short, Walker checked all the boxes that Republicans wanted after a disappointing loss in 2012. And it turns out that none of that mattered as much to Republicans three years later as putting a thumb in the eye of the party's establishment. Voters are turning to outsiders in a reaction to a lack of action, real or perceived, from the Republican Party after winning two midterm elections.

It's still early, and populist crushes usually don't last very long. Voters might start taking a second look at the up-and-coming generation of Republican leaders and give them a chance to succeed in the White House where Capitol Hill has failed them. When that moment comes, Walker might still be best positioned to capture their imagination. But he and his team need to prepare better for that moment when — and if — it comes.