I just want to underscore Elliott's point about how hard polling has gotten with a quick story I wrote up in a paper with Tori Gorton called "On the Internet, No One Knows You're An Activist." We were trying to survey lower-engagement voters, so we drew a sample of 9,937 registered Pennsylvania voters who hadn't consistently voted 2012-2018. Then, we matched them to Facebook accounts and served ads to 1,321 inviting them to take a survey. 66 people clicked on our ad, 7 began the survey, 6 completed it, and 1 person left an email for follow-up. I of course want to express my deep gratitude to that one respondent. But beyond that, a 0.4% response rate magnifies sampling errors, because very small differences in people's willingness to take polls can add up to very large errors in vote margins. That's especially true in primaries, where pollsters can't use partisan identification to stabilize the results.

—Dan Hopkins, 538 contributor

We've been tracking Trump's non-incumbent endorsees (because endorsing the incumbent is kind of a gimme) tonight, and so far he's 4 for 4 of the races called. Addison McDowell, Trump's pick in North Carolina's GOP primary for the 6th District, is also leading. But in California, state Assemblyman Vince Fong, who received Trump's endorsement for the Republican primary in the state's 20th District (Kevin McCarthy's old seat), is trailing at 26 percent with 23 percent of the expected vote reporting.

—Kaleigh Rogers, 538

It has become somewhat of a theme of our live blogs this primary calendar to note that Trump's challengers are beating their polls. This first looked to be the case in New Hampshire, where polls significantly underestimate support among Republican likely voters for Haley. But the pattern is more robust than one state: In fact Haley has been beating her polls by an average of five points (in vote share) once you account for undecided voters in these surveys. The consistency of this pattern is striking enough to warrant a post on the matter.

As Mary said earlier, polling primaries is hard! That is betrayed by the fact that POTUS primary polls are by far the least accurate type of poll in 538's pollster rating database going back to 1999. But error is different than bias, and when most of the polls are off in the same direction, something has gone awry.

That "something" is likely the difficulty in obtaining opinions of moderate Republicans from samples of "likely Republican primary voters." Remember that fewer than one percent of people called for a poll actually complete the interview. That means the ones that do are statistical "weirdos" (excuse the technical language). Pollsters adjust for this by weighting their samples to known population benchmarks — like the percent of all adults who are white, over 65, have a college education etc. But in primaries, such benchmarks do not actually exist; pollsters are just making educated guesses about them.

My theory is that most of these primary polls pulling samples of voters from voter registration lists are missing moderate crossover partisans and first-time voters. Additionally, we know that people who are highly motivated to participate in polls (the "weirdos") also happen to be the most politically and ideologically extreme Americans. That's a recipe for polling bias in primaries, where weighting to party, past vote and polarized demographic benchmarks does not control for the partisan consequences of overrepresenting politically engaged Americans.

Now, none of this is to say that polling is "broken." It's just hard to precisely sample a population that doesn't really exist. The polls for the 2024 primary still have below-average error, historically speaking, so we shouldn't go throwing out the baby with the bathwater. But this could nevertheless be a sign of pollsters having a hard time reaching moderate "normie" voters. And if that persists, it could have consequences for general election polls too.

—G. Elliott Morris, 538

In California's 40th District, with 46 percent of the expected vote in according to the Associated Press, engineer Allyson Damikolas (endorsed by EMILY's List), is trailing former fire captain Joe Kerr (endorsed by the Congressional Progressive Caucus PAC). The 40th is a key target for Democrats, who are looking to win back some of the ground they gained (and then lost) in the Orange County area. The 40th District spans Riverside and San Bernardino Counties, too.

—Meredith Conroy, 538 contributor

Since about the mid-1990s, Democrats have been electing more women to Congress than Republicans, and the difference grows bigger each cycle. This has a lot to do with the supply of candidates — more women identify as Democrats, and the women in the pool of traditionally "qualified" candidates (college-educated, in white-collar professions) are likely to lean Democratic. There's also the issue of demand — Democrats are more than twice as likely (75 percent to 29 percent) than Republicans to agree that there are too few women in politics.

These supply and demand issues may be mitigated if the Republican Party's organizational arm and donor class actively recruited, endorsed and financially backed women in primaries for competitive, or safe, red seats in November. This is the playbook Democratic PAC EMILY's List has been working from for years to elect more Democratic women to Congress and governorships. According to academic researchers, Democratic groups designated to elect more women are more likely to be prioritized by their donors than their Republican counterparts, which helps explain their success.

Although the GOP doesn't have a heavyweight equivalent to EMILY's List (which spends millions each cycle), there are groups committed to electing more Republican women to Congress. A couple of prominent new groups (Winning for Women and Elevate PAC) cropped up after the 2018 election, which elected 42 new women to Congress, but only four that were Republican. As a result, in both the 2020 and 2022 cycles, more Republican women ran in primaries than ever before, according to the Center for American Women and Politics.

But more women running doesn't always translate into more women winning. As we wrote ahead of the 2022 midterm elections, more Democratic than Republican women were nominated to run that year in House and Senate races where their party was either competitive or favored to win. While the GOP may have run and endorsed more women in primaries, it didn't emulate Democrats' strategy of actively recruiting women to run in races where they could win in November.

Today, there are just a few non-incumbent Republican women competitive for nominations in races they'd have any shot of winning in November. In Alabama's 2nd District, an incumbent-less primary due to redistricting, four of the eight Republicans running for the nomination are women. Of those women, attorney Caroleene Dobson has been endorsed by the women-focused VIEW PAC. Neither Trump nor the party committee has endorsed any candidate in that primary, but Dobson faces tough odds winning the crowded primary, and even tougher odds in a general expected to heavily favor Democrats.

11 Republicans are competing in Texas's 26th District, another race with no incumbent. Of two women in the race, Luisa del Rosal, a small business owner and former congressional chief of staff, has been endorsed by VIEW PAC. But she will have to defeat Trump endorsee Brandon Gill (who's also endorsed by the Club for Growth). The Republican woman running today with the most likely path to victory is former Rep. Mayra Flores: she's running to reclaim Texas's 34th District, the seat she won in a 2022 special election but lost in the general election later that year. She is endorsed by both Trump and VIEW PAC, which bodes well for her to face Democratic incumbent Vicente Gonzalez in a competitive general.

—Meredith Conroy, 538 contributor