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

Sitting governors and attorneys general don't usually openly try to defeat incumbents of their own party, but Texas Gov. Greg Abbott and Attorney General Ken Paxton are just built different, I guess. Today's Texas primaries are the culmination of two separate intraparty power struggles from the past year, in which Abbott and Paxton are actively trying to defeat Republicans who have defied them in the state legislature.

In May 2023, the Texas state House impeached Paxton on charges of bribery and abuse of office. He was later acquitted by the state Senate, but he has embarked on a revenge tour against those who supported his impeachment by endorsing primary challengers to 35 incumbent Republicans.

Meanwhile, Abbott suffered a massive political defeat last year when a group of mostly rural Republican legislators blocked his top priority, a school voucher program. In what the Houston Chronicle has called a "legacy-defining" campaign, Abbott has spent more than $4 million trying to oust 10 anti-voucher Republicans running for reelection.

Even Trump has gotten in on the act: He has endorsed at least eight primary challengers to sitting representatives, all of whom either voted against vouchers or voted to impeach Paxton (who is a close Trump ally).

If Paxton, Abbott and Trump are successful, the Republican caucus in the Texas state House will look very different — and further right — next year. Throughout the night, I'll be watching for how many incumbents they successfully topple.

—Nathaniel Rakich, 538