NASA astronauts Jasmin Moghbeli and Loral O'Hara voted in today's primaries ... from outer space. The two have been orbiting the earth aboard the International Space Station for roughly six months, but both still found a way to exercise their civic right.

—Cooper Burton, 538

Four years ago, Super Tuesday was one of the last big news events before the declaration of the COVID-19 pandemic. Just days later, the U.S. and much of the world would go into lockdown in an effort to stem the virus's spread.

As Julia noted, in 2020, Super Tuesday marked the point when the Democratic Party consolidated behind Biden. But I think that, partly because of the pandemic, even close observers of American politics don't appreciate just how unlikely Biden's Super Tuesday comeback was.

This year in Iowa, Ron DeSantis's second-place finish with 21 percent of the vote was enough to effectively end his campaign. But in 2020, Joe Biden came in fourth in the Iowa Democratic caucuses.

Similarly, pundits have viewed Trump as the prohibitive favorite in the 2024 race since at least his New Hampshire victory, when he topped Haley 54 percent to 43 percent. In 2020, however, Biden's New Hampshire performance was far weaker than Haley's this year — he finished fifth in the state, winning just 8 percent of Democratic primary voters.

But in a very short period four years ago, Biden resurrected his campaign. He convincingly won South Carolina on Feb. 29 thanks to his strength with Black voters, who had been few and far between in Iowa and New Hampshire.

Then, both Amy Klobuchar and Pete Buttigieg endorsed Biden in the run-up to Super Tuesday, consolidating the more moderate side of the Democratic Party against Bernie Sanders. That, in turn, positioned Biden for a decisive Super Tuesday win that made him the front-runner in short order. While Sanders won California, Biden won 10 states, including Massachusetts, North Carolina and Texas.

What explains the dramatic change in Biden's fortunes over a few short days leading up to Super Tuesday in 2020? In his book "Learning from Loss," political scientist Seth Masket emphasizes the Democrats' overwhelming aim to defeat Trump, and to find a candidate who gave them the best chance of doing so. At the time, there was evidence that Biden ran better against Trump than other Democrats. Many Democrats were willing to follow the cues of party leaders about their most competitive candidate, and in doing so, they vaulted Biden to the nomination.

In this year's GOP primary, there's some evidence that Haley may be a stronger general election nominee than Trump. But in a late-November survey I conducted via YouGov, GOP voters overwhelmingly saw Trump, not Haley, as their strongest candidate, and there's no evidence that's changed. So on the Republican side, the grounds for a similarly sudden Super Tuesday switch just aren't there.

—Dan Hopkins, 538 contributor

Super Tuesday has over 40 years of history that are deeply entwined with a bunch of issues in the presidential nomination process. The term "Super Tuesday" was first used in 1980 but was promoted by Democrats in 1988 as a deliberate effort to give an advantage to more moderate candidates. This was a direct reaction to the idea that the party's 1984 nominee, Walter Mondale, had lost to Ronald Reagan because he was too liberal. This strategy didn't really work out, though, and Democrats ended up nominating another northern liberal, Michael Dukakis.

In other words, this early attempt at a Super Tuesday brought some of the disadvantages of a regional primary, reducing the amount of attention on individual states and pressuring states to move their primaries earlier without really strengthening the influence of the region. Another drawback was that, by trying to enhance Southern influence by holding contests early, Super Tuesday also contributed to the "front-loading" problem", or the issue of having too many delegates selected at the beginning of the primary calendar.

Over time, Super Tuesday has taken on other significance as an important turning point in the race. As party politics scholar Caitlin Jewitt noted, in 2016, everyone thought that Sen. Ted Cruz needed to do well on Super Tuesday, which was heavily concentrated in Southern states where he needed to rack up wins — and when that didn't happen, it was a significant blow to his candidacy. For Biden in 2020, Super Tuesday marked the point when the party consolidated behind him. And in 2008, Super Tuesday made it clear that the Democratic nomination was a real race between Hillary Clinton and Barack Obama, as neither one scored a decisive victory.

It's hard to know exactly how this will play out in 2024. Republicans don't have the same ideological history with the big primary day as Democrats do. But the potential for a turning point in the race is there: Because so many delegates are at stake today, unless Haley wins a significant share of them, it may not make sense for her to stay in the race after tonight.

—Julia Azari, 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

The biggest downballot race in California is its U.S. Senate contest. Although 27 candidates filed for the race to fill the seat of the late Democratic Sen. Dianne Feinstein — who died last fall — the four leading contenders are Democratic Reps. Adam Schiff, Katie Porter and Barbara Lee, plus Republican Steve Garvey, a former Major League Baseball player. The front-runner appears to be Schiff, who is polling at around 25 percent in 538's California primary polling average. This puts him just a bit ahead of Garvey and Porter, who are right around 20 percent for the coveted second spot. Behind them is Lee, who is polling just under 10 percent.

The race has largely centered on Schiff and Porter, both of whom are fundraising powerhouses. As of Feb. 14, Schiff had brought in $29.8 million in net contributions, while Porter had collected $16.7 million, putting them each well ahead of Lee ($4.8 million) and Garvey ($2.1 million). The two leading Democrats also brought over huge sums left over from their House accounts — $21 million for Schiff and $7.4 million for Porter.

In the final weeks, Schiff has tried to use his massive campaign war chest to push Garvey into second place. Schiff has run ads that attack Garvey for his conservative views and past support for Trump, but the spots intend to raise Garvey's profile among Republican voters. By doing that, Schiff could help Garvey consolidate the GOP vote and finish ahead of Porter, relieving Schiff of a demanding general election campaign against the fellow Democrat. A pro-cryptocurrency super PAC may also help Schiff out, after swooping in with $10 million in outside spending seeking to derail Porter.

—Geoffrey Skelley, 538