I actually don't think polls are overestimating Trump by much, more that they're underestimating Haley. And I think it really comes down to undecided voters. Trump is a known quantity for pretty much everyone in America. So anyone who isn't sure if they're going to vote for him isn't unaware of his issues, but probably has some doubts about him. So my theory is that undecided voters skew, if not anti-Trump, at least Trump-skeptical and are disproportionately choosing Haley. You can see an inkling of that in the preliminary exit poll data: In Virginia, for example, voters that decided their vote choice earlier than this year went overwhelmingly for Trump (78 to 21 percent), but voters that made their decision later chose Haley (54 to 42 percent).

—Mary Radcliffe, 538

Polling nowadays is incredibly hard. Seeing response rates of under 2 percent is all too common. So even very slight differences in how fired up people are to take polls can translate into meaningful differences between polls and results. Primary polling is especially hard because you can't use partisan identification to benchmark how reasonable the sample looks. That all said, in New Hampshire and in South Carolina, I wonder if Haley may have benefited from the lack of a competitive Democratic primary, and the fact that some who might have otherwise voted in a Democratic primary were able to vote for Haley.

—Dan Hopkins, 538 contributor

What's everyone's favorite theory about why polls have seemed to consistently overestimate Trump support? (I know this was discussed some on the podcast.)

—Julia Azari, 538 contributor

Tonight I'll also be watching my home state of Arkansas, where polls just closed. There hasn't been recent polling on the GOP presidential primary there, but Trump remains popular in the conservative state, which he won 62 percent of the state in the 2020 general election. His former press secretary is the governor, Gov. Sarah Huckabee Sanders, and she endorsed him in the fall.

There's not much suspense downballot either. Rep. Steve Womack, who represents the northwest corner of the state—home to the University of Arkansas, Walmart, and other big businesses and booming towns—is fending off an unlikely challenger from his right and is the only Republican incumbent to face a challenger. That challenger, State Sen. Clint Penzo is against vaccines, the war in Ukraine, government spending and has criticized Womack's votes during the House speaker fight last fall. But Womack has represented the district for 13 years and all the advantages of incumbency.

On the Democratic side, all four candidates for the House are running uncontested.

Perhaps of a bit more interest — earlier, I wrote about the state Supreme Court races and how the outcomes there could result in a game of musical chairs leading the very conservative Sanders to make one or two appointments to the court.

—Monica Potts, 538

Minnesota Rep. Dean Phillips ended his campaign for president today and endorsed Biden's reelection campaign. Phillips got into the race last fall, citing Democratic worries about Biden's age and ability to beat Trump. But his campaign never took off, even in New Hampshire, where he focused much of his efforts because Biden wasn't on the ballot due to the state's primary having violated the national Democrats' new calendar rules. Phillips won 20 percent of the New Hampshire vote, but he didn't clear 10 percent in any other state where he got on the ballot. Yesterday, he earned 8 percent in his home state of Minnesota and 9 percent in Oklahoma, his best showings otherwise.

Although some Democrats share Phillips's concerns about Biden, Phillips predictably struggled because the incumbent president remains relatively well-liked by those in his party. Phillips was an unusual primary challenger in that he didn't have sizable ideological disagreements with Biden that stoked his run — the moderate congressman was not from the Bernie Sanders wing of the party, for instance. And Phillips's overall performance reflects the lack of appetite for a center-left alternative to Biden — who hails from that part of the party — or at least one who didn't already have a sizable standing. Rather, the intraparty dissatisfaction with Biden has been felt more on the left, which has been especially critical of Biden's handling of the Israel-Gaza situation. (See: the "Uncommitted" protest movement getting more votes than Phillips in his home state.) Tellingly, Marianne Williamson's minor left-wing campaign has actually won more votes than Phillips in 10 of the 15 primaries they both participated in.

—Geoffrey Skelley, 538