The upshot of the Bernie Sanders and Donald Trump phenomena is that both parties are moving to the left.

Sanders’ and Trump’s styles and affects are very different — the rumpled, oddball lecturer in Socialism 101 vs. the boastful, power-tie-wearing business mogul — but they have worked in tandem to ensure that the center of gravity in this fall’s presidential election will be further to the left than it has been in decades.

By seizing the initiative in their race from the beginning to what looks like an increasingly bitter end, Bernie Sanders has made Hillary Clinton, the cautious inheritor of a family political legacy built on centrism, into the mouthpiece of a watered-down version of his left-wing populism.

No matter how much Bernie Sanders hates the banks, Hillary Clinton despises them just as much (past paydays notwithstanding).

In effect, Sanders and Trump have executed a squeeze play on the Madam Secretary. Sanders pushed her to the left on trade and Social Security in the primary, when she disavowed the Trans-Pacific Partnership that she helped negotiate and embraced increasing Social Security benefits. She probably won’t be snapping back to the center on those issues in a general election because it would open her up to Sanders-like attacks from Donald Trump.

Such is the shift in the tectonic plates of our politics that the presumptive Republican nominee for president, endorsed by voices on the right ranging from Sean Hannity to Mitch McConnell, is making a far-fetched but not entirely irrational pitch for the support of fans of a Vermont socialist.

It’s unlikely that anyone currently “Feeling the Bern” is going to shift to wanting to “Make America Great Again.” Trump’s un-PC pronouncements alone are presumably enough to repel Sanders supporters. Yet there is enough overlap in Trump and Sanders — the protectionism and noninterventionism, the belief that the political and economic system is rigged — that Trump might as well give it a try.

If the grass-roots movement that Sanders has built will pressure Democrats all the way to the Philadelphia convention and beyond, Trump has arguably done more to pull the country’s politics portside. He has, for now, managed to do what the Democrats and the media have been attempting for most of the Obama era: to kill off the tea party as a national force.

By dividing it, eclipsing it and making its animating concerns of limited government and constitutionalism into afterthoughts, Trump has neutered a heretofore potent vehicle against Big Government. With or without Sanders, the Democrats were going to drift in a more progressive direction. It was far from inevitable, though, that the Republican Party would de-emphasize its opposition to growth in the size of government. That is entirely the doing of Trump.

The irony is that an era of Republican politics characterized by insistence on doctrinal purity and anger at Beltway dealmaking is ending with Trump at the helm of the GOP. It’s a little like the agitation of the French Revolution, all aimed at achieving more liberte, egalite, fraternite, concluding in the rule of Napoleon Bonaparte.

However ideologically indistinct Trump was during the primaries, he has gotten fuzzier since becoming the presumptive nominee. The lazy line on Donald Trump is that he’s a far-right populist. Not at all. He’s a centrist populist.

The key to moving the GOP to the center wasn’t high-minded scolding about its tone and unreasonableness, as Jon Huntsman, John Kasich and Jeb Bush all attempted, but an extremely combative tone and a few signature unreasonable positions. Once Trump established his reputation as a bomb-thrower, it didn’t matter that he was to the left of everyone else in the field or promised to spend most of his time as president cutting deals.

Between Sanders moving Clinton further from the center and Trump moving the GOP toward it, the socialist and the mogul have forced American politics to take a collective step to the left.

Rich Lowry can be reached via e-mail: comments.lowry@nationalreview.com.