PHOENIX — In a span of about 12 hours, Americans were given definitive evidence that the Republican Party is now in thrall to its most ideologically and tactically extreme forces while the Democrats still look to the center ground and to compromise.

Exhibit A: The results of Tuesday’s primaries. Exhibit B: President Obama’s nomination of Judge Merrick Garland, as moderate and consensus-building a choice as he could have made, to the Supreme Court.

In the electoral showdowns, Donald Trump pulled off a near sweep. Yes, John Kasich, the most underrated candidate all year, managed to beat Trump in Ohio. But Trump defeated his opposition everywhere else and put a Jeb-like exclamation point on the day by trouncing Marco Rubio in his home state of Florida.

GOP establishmentarians had anointed Rubio as their savior, figuring the young Cuban-American could cloak his very conservative positions under the appealing mantle of youth and diversity. It didn’t work.

Rubio learned that trying to be everyone’s backup choice rarely wins you first place. And members of an increasingly angry and overwhelmingly white Republican electorate have been told for seven years by their leaders that Obama is a radical trying to turn America into a foreign place. In large numbers, they heard what their party was saying and voted accordingly — for the candidate who most plainly echoes their extreme rage and alarm.

Democrats, on the other hand, moved toward the center. Hillary Clinton won resoundingly in Florida, North Carolina and, most significantly, Ohio. She narrowly defeated Bernie Sanders, her outspoken progressive rival, in Illinois, and apparently also eked out a popular-vote win in Missouri.

Sanders, already here in Arizona on Tuesday campaigning for the state’s primary, will continue to influence the nation’s political debate by highlighting the issues of economic inequality and the pro-wealthy, pro-corporate bias of our corrupting campaign finance system.

But when it came down to it, Democratic voters chose the candidate they told exit pollsters was offering realistic policies for the future. Clinton may well have gained ground among temperate and peaceable voters who were appalled by Trump’s extremism, the disruption he incites at his rallies and his mind-boggling egotism. On Wednesday, he said on “Morning Joe” that when it comes to consulting on foreign policy, “I’m speaking with myself, number one, because I have a very good brain.”

Trump’s narcissism could not have contrasted more starkly with Garland’s unforced humility and his insistence on crediting others for his successes at the Rose Garden ceremony where Obama introduced him. For the record, Garland has been a friend for more than 40 years and is, quite simply, one of the most decent people I have ever known.

But put aside his personal qualities and look to the choice the president has made. Of all the options he had before him, Garland was the most middle-ground candidate available, someone who received 32 Republican votes when he was confirmed to the D.C. Circuit Court in 1997. He’s a well-known believer in judicial restraint, the quality Republicans claim to revere in judges. Many progressives wanted someone to Garland’s left. Obama instead went out of his way to pick the person so many Republican senators had said would be their favorite among potential Democratic nominees.

Oh yes, and for those who claim that Obama is trying to tilt the court in a liberal direction for generations, Garland, at 63, was also the oldest choice among the reported finalists.

And how did Republican senators respond to Obama’s moderation? With the same obstruction that has characterized their answer to so many of the other olive branches he proferred over the course of his presidency. And why should we be surprised? This, after all, is the same crowd that happily coddled Trump when he was challenging Obama’s very right to hold office with lies about the president’s birth certificate.

To stay on the respectable side of Washington opinion, commentators regularly retreat to bromides about how “both parties have become more extreme.” It’s bracing to see this evasion of reality slapped in the face by the nation’s primary voters and by the Republican leadership’s Trump-like rejection of the very sort of Supreme Court nominee they once said they’d gladly embrace.

E.J. Dionne is a columnist for The Washington Post. His email address is: ejdionne@washpost.com. Twitter: @EJDionne.