The only thing predictable about the 2016 presidential campaign so far has been its unpredictability.

A year ago, Democrat Hillary Clinton and Republican Jeb Bush were their respective parties’ front-runners and presumed nominees. Now, Donald Trump continues to hold a commanding lead in national polls for the GOP nomination, and Bernie Sanders, the independent senator from Vermont who is a self-proclaimed socialist, is poised to beat Clinton in the upcoming Iowa caucus and New Hampshire primary.

Could Trump and Sanders face off in the general election? What would it mean for the Democratic and Republican parties? What would it mean for the country? Ben Boychuk and Joel Mathis, the RedBlueAmerica columnists, think the unthinkable.

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JOEL MATHIS:

The fact that we’re even contemplating a Sanders-versus-Trump election proves one thing: The electorate has started to reach its polarized limits.

Decades ago, both parties spanned fairly broad sections of the ideological spectrum. It’s how Democrats could be the party of Southern segregationists and the authors of the Voting Rights Act; it’s how Republicans could keep middle-of-the-road Dwight Eisenhower in office for eight years and nominate conservative firebrand Barry Goldwater to the presidency just a few years after that.

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That meant overlap: The most conservative Democrat in Congress back in those days was often somewhere to the right of the most liberal Republican.

The last few decades have dispensed with that order. Study after study shows that the electorate has sorted itself into increasingly homogeneous parties: If you’re liberal, you’re a Democrat. If you’re conservative, you’re Republican. The overlap is gone.

The result? You’re getting to see the parties in their essences. You get to see the fruition of ideas and their logical consequences.

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For Republicans, it means that decades spent whipping up right-leaning voters into an angry hysteria - thanks to talk radio, Fox News and online outlets like Breitbart - has paid off with widespread support for a candidate whose appeal boils down to snarling, offense-giving tribalism, the pinnacle of a career spent diminishing the fortune he inherited.

For Democrats, you’re seeing a desire to help the poor and middle class live financially sustainable lives. But Sanders’ heart may be bigger than his wallet: Vox’s Ezra Klein says Sanders’ proposed health care plan would require raising $1 trillion a year in taxes. Paul Krugman, no conservative, says it would probably require higher middle class taxes than Sanders is willing to admit. It’s hard to believe the American electorate has much stomach for that.

It’s easy, and wrong, to make a fetish of centrism and compromise. In our politics, the best ideas tend to flow to the middle, not from it. But the system gets bogged down without some moderate good sense in the mix. A Trump-versus-Sanders race suggests we’re dire need of more good sense.

BEN BOYCHUK:

Readers of a certain age and disposition will remember a Marvel Comics series from the late 1970s and early ’80s called “What If . ?” The gimmick was to take a story from the main continuity of Marvel’s comic book universe and put a different spin on it. “What If Spiderman Joined the Fantastic Four?” “What If The Avengers Had Fought Evil During the 1950s?” “What If Captain America Had Been Elected President?”

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The 2016 presidential election feels like a “What If . ?” story.

What if the Republican Party base revolted? What if the presumed nominee of the Democratic Party collapsed under the weight of her scandalous past and present?

Sanders’ persistence as a candidate and credible challenger to Clinton is as remarkable as Trump’s persistently high poll numbers. The socialist from Vermont has raised more than $76 million for his campaign, mostly from small donors. She’s raised more money, but he’s drawing support from a broader base.

You think the conservatives are angry and divided? The fact that Sanders is within striking distance of Clinton in Iowa and looks to be crushing her in New Hampshire speaks to how cranky and dissatisfied the Democrats’ more left-wing base has become. And with word this week that the State Department inspector general found highly sensitive classified information among Clinton’s personal emails, her troubles can no longer be brushed off by the campaign as right-wing paranoia (which was always a fib).

What’s interesting about the prospect of a Trump-Sanders election, though, is the reality of the choice American voters would be asked to make. Trump is no conservative. He’s barely a Republican. He’s a nationalist first and foremost. So is Sanders.

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A Trump-Sanders matchup would make for a wild “What If . ?” tale. What if Americans have to choose between two candidates who dislike free trade, love higher tariffs on foreign goods, and want to restrict legal and illegal immigration? What if the choice is between a candidate who would cut taxes and add trillions to the deficit and a candidate who would raise taxes and add trillions to the deficit?

Mister, we could use a man like Captain America again.

Ben Boychuk (bboychuk@city-journal.org) is associate editor of the Manhattan Institute’s City Journal. Joel Mathis (joelmmathis@gmail.com) is associate editor for Philadelphia Magazine.