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

As I mentioned earlier, 2018 was a watershed year for political ambition among Democratic women. Not only did Democratic women run in record numbers in 2018, they also outperformed Democratic men in their primaries. And in November of that cycle, female candidates were responsible for more than 60 percent of the congressional seats that flipped from red to blue. That year was a nail in the "women aren't electable" coffin.

There are a few Democratic women running tonight who are vying to do just that once again.

In southern California's 40th District, which spans parts of Orange, Riverside and San Bernardino counties, engineer Allyson Muñiz Damikolas is hoping to face Republican incumbent Young Kim in November. Kim herself was one of the few Republican women who won in 2020 when she flipped California's 39th District by less than 5,000 votes Due to redistricting, Kim ran in the 40th District in 2022, where she won by a much larger margin. Still, this region of California is in flux demographically and politically, so it makes sense as a target for Democrats. EMILY's List is backing Muñiz Damikolas, but to advance to November, she'll need to get past fellow Democrat, retired fire Capt. Joe Kerr, first, who has been endorsed by the Congressional Progressive Caucus PAC.

Next, in Texas's 15th District, small business owner Michelle Vallejo is favored to advance tonight to a rematch against Republican incumbent Rep. Monica De La Cruz. Vallejo, who has endorsements from EMILY's List and the DCCC, lost by nearly nine percentage points in 2022, but Democratic groups have invested more in the race this time around as a top pickup opportunity. And in California's 3rd District, wildfire specialist Jessica Morse is running to face the Republican incumbent, Rep. Kevin Kiley. Morse is endorsed by EMILY's List, but not the DCCC. She and Kiley are likely to advance out of today's top-two primary, which includes a third-party candidate.

In addition to these, there are several bluer districts with incumbent-less primaries today where Democratic women will be competitive:

- Rep. Colin Allred is running for Senate, opening his seat in Texas's 32nd District. State Rep. Julie Johnson has support from EMILY's List and seems to be one of the top two candidates in a crowded Democratic primary.

- Rep. Tony Cárdenas announced his retirement in his blue San Fernando Valley district (California's 29th). Luz Maria Rivas, who has support from EMILY's List and the Congressional Progressive Caucus PAC, should finish in the top two today.

- Rep. Barbara Lee isn't running for reelection in California's 12th District, instead vying for the Senate. Organizer and civil rights activist Lateefah Simon is a clear front-runner. She has Lee's endorsement, as well as Gov. Newsom's, and backing from EMILY's List.

- Rep. Anna Eshoo announced her retirement after three decades in Congress, opening up California's 16th District. EMILY's List is backing former Stanford dean Julie Lythcott-Haims, but she's caught in a tight race with four other strong candidates who have her beat on the spending front.

- Rep. Katie Porter is also running for Senate instead of reelection in California's 47th District. Lawyer Joanna Weiss, who has an endorsement from EMILY's List, looks to be in a contentious race with state Sen. Dave Min to become the Democratic flagbearer this fall.

Given that Lee, Eshoo and Porter are women and not all of today's female candidates are favored to advance, today's races mainly give Democratic women a chance to maintain the progress they've made in recent cycles.

—Meredith Conroy, 538 contributor