President Donald Trump may be the de facto leader of the G.O.P., with Kim Jong Un–like control over Fox News, a cult-like following in the hinterlands, and more than $100 million already banked for his re-election campaign, but the loyalty of the Republican rank and file is not without its limits. When conservative lawmakers were last pressed to say whether they would endorse the president in 2020, many demurred: “I don’t know what the world is going to look like,” Senate Majority Whip John Cornyn told CNN in April. “Look, I’m focused on opioids,” said Senator Lamar Alexander. Retiring Senator Bob Corker, who knows full well that Trump has already formally declared he is running for re-election, insisted that he has “no idea whether the president will run for re-election nor what the field will be on the Republican side.”

Since then, the state of play has only darkened for the president. There are currently 17 known investigations targeting Trump and his associates, dozens of House Democrats itching to unleash subpoenas, an unresolved trade war, and a potential recession on the horizon. No wonder Senate Republicans still sound unready to endorse Trump. “I see nothing wrong with challengers—that is part of our democratic system,” Senator Susan Collins said Sunday on CNN’s State of the Union. She declined to endorse a candidate—“I’m going to talk about 2020 in 2020”—though she noted that any potential Republican-primary challengers “would have an uphill climb.”

The problem, as a new poll out of Iowa vividly illustrates, is that there are no white knights the Republican electorate prefers to Trump. While a whopping 63 percent of registered Iowa Republicans told the Des Moines Register that they would welcome a primary challenger in 2020, no theoretical candidate comes close to Trump’s (sinking, but still high) 81 percent approval rating. The next three most popular Republicans—Ted Cruz (68 percent), Mitt Romney (65 percent), and Marco Rubio (63 percent)—are unlikely to challenge Trump. Republicans who might do so, meanwhile, were so unpopular they may as well have been Democrats. Senators Ben Sasse and Jeff Flake, who frequently complain about Trump, despite voting with him at nearly every opportunity, registered a dismal 24 percent and 16 percent approval rating, respectively. Outgoing Ohio Governor John Kasich, who has been the most outspoken about running, was viewed favorably by only 31 percent of Iowa Republicans.

In short, Iowa Republicans might say, President Trump is the worst presidential candidate except for all the other ones. “If there is no better candidate, I would vote for President Trump again,” one Iowan who was polled told the Des Moines Register. “But if there is somebody—another Republican who maybe has better ideas about trade or ways to help out the [agricultural] sector, and not have so many political tensions—I would definitely consider voting for them.”

Of course, a successful primary challenge would require a revolt in Washington, too. And thus far, even retiring Republican lawmakers aren’t prepared to offer anything more than the most tepid criticisms. Last week, when Orrin Hatch was asked to comment on allegations that Trump had committed a felony by breaking campaign-finance law, the outgoing senator said, “I don’t care. All I can say is he’s doing a good job as president.”

Hatch later walked back the remark, but it was indicative of where the party currently stands. Trump, as Senator Corker told MSNBC’s Kasie Hunt in an interview Sunday, is an “anomaly” who doesn’t represent what Republicans have traditionally been about. But when asked directly whether he would call for a primary challenge against the president, he dodged. “We’ve got to remember what the Republican Party is,” said Corker, who is retiring from Congress in January. “I want to get away from here and think about that.” Even a man who previously described Trump as mentally unfit to serve as president wasn’t ready to renounce him—at least not until somebody better comes along.

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