Maryland Gov. Larry Hogan (R) in Annapolis on Nov. 7, 2018. (Patrick Semansky/AP)

Stephen F. Hayes is the former editor in chief of the Weekly Standard.

Elizabeth Warren was just in Iowa. Cory Booker’s been hanging out in New Hampshire. Julián Castro is giving interviews to anyone who asks. Beto O’Rourke is planning a meet-the-voters road trip. Bernie Sanders is doing damage control. And Joe Biden is publicly wondering whether Democrats need an elder statesman with the qualifications and experience of, say, someone like Joseph R. Biden Jr. to carry the party to victory in 2020.

On the Republican side of the 2020 presidential election, however, it’s relatively tranquil. Sure, there’s John Kasich’s voluble consultants trying to encourage a Draft Kasich movement for the two-time also-ran who has lately been abandoning many of his conservative positions in favor of oatmeal centrism that might have broader appeal. Nikki Haley’s resignation as United Nations ambassador generated several hours of speculation before she promised she’d eagerly campaign for President Trump’s reelection. A strong anti-Trump op-ed recently in The Post by Mitt Romney read like something of a tryout for the Leader of the Opposition. But the 2020 speculation it stoked died down quickly after Romney told CNN’s Jake Tapper, “I’m not running again.”

In some respects, the quiet among Republicans isn’t surprising. The incumbent president is a Republican. Serious intraparty challenges at the presidential level are relatively rare and never successful.

But the Republican president is Donald Trump. If ever there were a time for a serious intraparty challenge, it’s now. He has strong support from elements of the Republican base, but he has alienated virtually everyone else, especially those segments of the electorate that are growing the fastest. The ideal challenger would be a committed, articulate conservative — maybe a governor, such as Maryland’s Larry Hogan, or a senator, such as Nebraska’s Ben Sasse — who would make a case for limited government that will otherwise go unmade, and who would show voters that conservatism and Trumpism are not one and the same.

The 2018 midterm elections were a clear and unmistakable rebuke of the chaos of his first two years as president. And it’s getting worse. The final few weeks of this second year of his presidency are proving even more chaotic than the first hundred weeks.

Trump’s steady stream of lies has picked up over the past six months. His Twitter feed is more unhinged. His sudden Syria withdrawal announcement on Dec. 19 surprised everyone from allies to the military leaders who would be tasked with carrying out his order. His recent unprompted defense of the 1979 Soviet invasion of Afghanistan was enough to make even paid Putin apologists blush. As special counsel Robert S. Mueller III’s investigation draws closer to the Oval Office, it is clearer every day why Trump fired Attorney General Jeff Sessions for failing to protect him from the inquiry.

Now, Trump is threatening to declare a “national emergency” and use “the military version of eminent domain” to secure the southern border — a stark admission that he has failed on his central campaign promise: to build a wall and make Mexico pay for it.

There’s reason to believe this will all get worse over the next year. The Mueller investigation is testing whatever sanity Trump still possesses. Democrats controlling the House will use their newfound power to investigate every corner of the Trump administration — an administration already marked by malfeasance and corruption. Two of the men credited with constraining Trump’s most destructive impulses over the first two years — Defense Secretary Jim Mattis and White House Chief of Staff John F. Kelly — have left the administration. Perhaps most ominous for Trump’s political fortunes, a growing number of economists are predicting a slowdown of the U.S. economy — threatening the one issue where wins Trump positive numbers.

The “Trump Tracker” from Morning Consult found that Trump’s net approval rating fell in 43 states in December. Nationally, his approval rating is stuck in the high 30s or low 40s, depending on the poll. By a margin of about 20 points, more Americans believe the country is headed in the wrong direction than on the right track. An NBC poll from December found that 38 percent of registered voters say they will definitely (23) or probably (15) vote for Trump if he runs for reelection, while 52 percent say they will probably (13) or definitely (39) vote for the Democrat in the general election.

Trump’s conservative supporters point to his accomplishments — tax reform, progress in the fight against the Islamic State, two Supreme Court justices, deregulation — and claim that they make the chaos and crazy worth it. A primary challenge could badly damage Trump’s general-election prospects and help elect a Democrat, they argue, and, in any case, everyone knows primary challenges never succeed.

Would a primary challenge really do more damage to Trump’s reelection effort than Trump has done himself? It’s hard to see how. And as Trump supporters should understand better than most, the volatility of the current political moment means that things “everyone knows” cannot happen sometimes do. For the good of the country, sometimes it’s vital that they do.