Trump has endorsed only three candidates in seriously contested primaries today: Moreno, Bost and Merrin. With all three locked in competitive races, tonight's results could be a good signal of whether Trump's endorsement is as powerful as it used to be. We'll be tracking these races throughout the night.

—Nathaniel Rakich, 538

One of today's most consequential primaries for the general election is taking place in Ohio's 9th District. According to Daily Kos Elections, Trump would have carried the district 51 percent to 48 percent in 2020. But in 2022, incumbent Democratic Rep. Marcy Kaptur defeated Republican Air Force veteran J.R. Majewski 57 percent to 43 percent here thanks to Majewski's weaknesses as a candidate: He exaggerated his military service, attended the Jan. 6 rally (though he says he didn't enter the Capitol) and once subscribed to the QAnon conspiracy theory.

Majewski quickly announced he would run again in 2024, agitating Republican operatives who feared he would once again throw away a winnable House seat. But to their relief, he withdrew from the race a few weeks ago, leaving the primary to state Rep. Derek Merrin and former state Rep. Craig Riedel. Riedel was originally the top alternative to Majewski, but a couple of his pro-Trump supporters withdrew their endorsement of him after audio leaked of him calling Trump "arrogant." That sent GOP elders scrambling to find a new alternative to Majewski, and Merrin — who was in line to be the speaker of the Ohio state House last year until a faction of renegade Republicans joined Democrats to elect a different Republican — jumped into the race just before the filing deadline.

The primary is far from settled, though. While Trump endorsed Merrin just yesterday, and Speaker Mike Johnson endorsed Merrin in January, many establishment Republicans, such as House Majority Leader Steve Scalise and Majority Whip Tom Emmer, are still with Riedel. And Merrin's late entry into the race means he trails Riedel badly in fundraising, $175,000 to $1.2 million. And while he's no Majewski, a Riedel win could still give Republicans headaches: He's aligned with the tea party movement and has previously expressed interest in joining the hardline House Freedom Caucus.

—Nathaniel Rakich, 538

Chicagoans are voting today on a ballot measure pushed by progressives that would institute a real estate transfer tax to fund programs addressing homelessness. Today's outcome could tell us something about the strength of Chicago's progressive movement … and its unpopular progressive mayor, who's made it a policy priority.

According to publicly available polling, while Chicagoans may have started out feeling good about Mayor Brandon Johnson, their opinion quickly soured. According to Chicago-based Victory Research, Johnson's approval when he first took office in May was at 63 percent. Five months later, in October, Echelon Insights/Illinois Policy Institute found his approval to be just 28 percent, with 50 percent of voters disapproving of his job performance. By January, Tulchin Research/Stand for Children registered an approval rating of just 21 percent, with 70 percent saying his performance was "only fair" or "poor," while Echelon Insights/Illinois Policy Institute marked his approval at 29 percent and disapproval at 57 percent.

The January Echelon Insights survey also asked respondents if they approved of Johnson's handling of various issues facing the city. The mayor received the lowest ratings on "housing and homelessness" (20 percent approve, 68 percent disapprove), "management of immigrants transported to the city" (23 percent approve, 69 percent disapprove), and "crime and public safety" (24 percent approve, 66 percent disapprove).

—Mary Radcliffe, 538

As Geoffrey mentioned, Fong is the front-runner in today's California 20th special election, and there's a chance he wins the seat outright today if he gets a majority of the vote. Other than Fong, perhaps no one is rooting for this outcome more than House Speaker Mike Johnson, whose Republican majority is currently paper-thin — and getting thinner.

Right now, the House has 219 Republicans and 213 Democrats, meaning Johnson can afford two Republican defections to pass legislation with a bare majority (three Republican defections would yield a 216-216 tie, which isn't enough to pass a bill). However, GOP Rep. Ken Buck recently announced that he would resign on March 22, which will bring the GOP majority down to 218-213.

If Fong wins outright today, he would presumably be sworn in around the same time that Buck leaves, keeping the Republican majority at 219-213. But if he doesn't, the soonest Fong (or another resident of the California 20th) could take office would be late May following a runoff. And in fact, an April 30 special election in New York's 26th District is very likely to send a Democrat to Congress, which would narrow the GOP majority to 218-214 if the California seat is still vacant. That would mean that, for a time, Johnson could only afford one Republican defection before his bills would fail! If you thought it was hard for House Republicans to govern before …

—Nathaniel Rakich, 538

With 68 percent of the expected vote reporting, Bost leads Bailey 53 percent to 47 percent in the Republican primary in Illinois's 12th District. But Bost looks to be on pace for a potentially narrower win — and perhaps could even lose. After the 2020 Census, Illinois Democrats drew a gerrymander that packed more Republican-leaning turf into Bost's 12th District in southern Illinois, which he had represented since 2015. About half of the new-look version of the seat had been in Bost's old district, but much of the eastern part of the seat was new to him. Meanwhile, Bailey's old state Senate seat made up a large chunk of that eastern section, giving him a geographical base of support for this primary despite facing the incumbent Bost.

As things stand, Bost is winning about 70 percent of the vote so far in the area he represented prior to the 2022 election, while Bailey is winning 73 percent in the counties that were in his old state Senate seat. The two are running about even in the remaining turf. The good news for Bost is that more of the primary vote will likely come from his neck of the woods. But the good news for Bailey is that more outstanding votes are likely left to be counted in his area of the district. A back of the envelope calculation based on each candidate's showing so far would put Bost up about 51 percent to 49 percent by the time all is said and done, but that is too close to call.

—Geoffrey Skelley, 538