Donald Trump
Donald Trump speaks with the Chicago Tribune Editorial Board Monday, June 29, 2015 in Chicago. Michael Tercha/Chicago Tribune/TNS via Getty Images

The 2016 general election isn't for another 460 days, but it's already defying expectations. Political pundits, media outlets and even the candidates themselves have become confounded by the way things are playing out, leading many to ask: Is the United States gearing up for a black swan election?

Candidates who were supposed to do well generally have not, especially the cluster of Republican governors who have tossed their hats into the ring. The most obvious example of this came Tuesday, when Fox News announced the lineup for the first GOP debate. Only the top 10 candidates were included in the primetime event, and several candidates considered to be front-runners weren't among them. For example, former Pennsylvania Sen. Rick Santorum -- who was neck-and-neck with eventual GOP nominee Mitt Romney in 2012 before he dropped out -- didn't make the cut. He wasn't happy.

"The idea that they have left out the runner-up for the 2012 nomination, the former four-term governor of Texas, the governor of Louisiana, the first female Fortune 50 CEO, and the 3-term Senator from South Carolina due to polling seven months before a single vote is cast is preposterous," Santorum spokesman Matt Beynon said in a statement to NBC News, adding that the process was "incredibly flawed."

The other candidates invited to what was referred to as a "kiddie table" debate early Thursday night were also suffering. Former Texas Gov. Rick Perry had only 1.8 percent support in the polls, despite enjoying relatively steady popularity while in office. Even after his 2014 indictment for allegedly abusing his power to punish a Democratic district attorney, he had a 57 percent approval rating. He's also had direct experience with border security, having deployed the National Guard last year to help handle the influx of immigrant families entering the country from Mexico.

But candidates who made the primetime lineup of Thursday's Fox News debate were also having trouble convincing their backers to make the jump. Sen. Rand Paul, R-Ky., should have launched his campaign directly into an expansive support network started by his father, ex-presidential candidate and former Texas Rep. Ron Paul. But he was in eighth place.

Former Florida Gov. Jeb Bush garnered only 12.5 percent support Tuesday despite his family history and deep pockets. He and his super PAC, Right to Rise USA, having raised $114 million for his campaign. For comparison's sake, Hillary Clinton and her allies have raised about $69 million so far, the Wall Street Journal reported.

The lone victor thus far seemed to be someone who's not a politician at all: Donald Trump. His popularity has proven especially vexing -- every time he's made a divisive statement predicted to sink his run, he's risen in the polls. In his campaign kickoff speech, Trump referred to Mexican immigrants as rapists and criminals, but a July Washington Post-ABC News poll showed that 33 percent of the general public liked him -- 17 percentage points higher than how he'd polled in May. He maintained his lead among likely GOP primary voters after mocking Sen. John McCain, R-Ariz., for being a prisoner of war in Vietnam.

"He obviously benefits from his celebrity, but ... there is a segment of the Republican electorate that is strongly anti-immigrant and there is an overlapping piece of the Republican electorate that is anti-politician," Democratic pollster Geoff Garin told the National Journal. "Donald Trump appeals to those voters, and not in the most sophisticated way possible, but in the loudest way possible."

The craziness hasn't just been confined to the Republican field. Many considered former Secretary of State Clinton, who conceded the Democratic nomination to now-President Barack Obama in 2008, a shoo-in this time around. But then Sen. Bernie Sanders, I-Vt., entered the race. A Monmouth University poll released Wednesday found Democratic support for Sanders was at 16 percent, second to Clinton's 52 percent. A WMUR/University of New Hampshire poll had the two candidates even closer: 36 percent of liberal respondents said they'd vote for Sanders and 42 percent said Clinton.

Vice President Joe Biden, who hasn't said whether he's planning to run, has also enjoyed a groundswell of support in recent weeks. He averages about 5 percentage points behind Sanders.

All of this means that it's unclear who will be the next president of the United States. The size of the Republican field combined with Democratic wildcards has made the run-up to the general election, which Americans have historically scrambled to predict, unpredictable. We'll just have to keep watching to see what happens next.

"What we have seen in recent general elections in the U.S. is that what matters most to voters is not whom you love, but whom you loathe," Emory University political scientists Alan I. Abramowitz and Steven Webster wrote for Sabato's Crystal Ball, a political analysis newsletter. "It promises to be a long and nasty campaign."