ABC News can now project that Trump will win the Colorado primary. With almost half the expected vote reporting already, Trump has 60 percent to Haley's 36 percent. It's Trump's eighth win of the evening already, and this one is particularly rough for Haley, as this was one of the few states where she had the best shot at an upset win.

—Nathaniel Rakich, 538

Polls have now closed in Minnesota, which was a sleeper battleground in the 2016 general election, but tends to support Democrats. There are a greater-than-average number of college graduates in the state, which should be good for Haley, but there's also a sizable white working class population, which, if you're reading this live blog, you probably already know, is good news for Trump.

—Jacob Rubashkin, Inside Elections

In one of the least surprising developments of the night, ABC News projects that Trump will win Alabama. Only 5 percent of the expected vote has reported there, but Trump leads Haley by a punishing 69-point margin, 83 percent to 14 percent. We expected Alabama to be one of Trump's strongest states, and that looks to be the case.

—Geoffrey Skelley, 538

Going into tonight, I thought that Colorado could be a dark horse state for Haley. There wasn't a single poll of the race there, and the state's highly educated demographics seemed like a good fit for her.

Well, so far, it ain't happening. With 28 percent of the expected vote reporting, Trump is taking 57 percent of the vote there, while Haley has just 40 percent.

—Nathaniel Rakich, 538

It’s the biggest day of the primary season, and former President Donald Trump could very well sweep all 15 GOP presidential nominating contests today. With limited polling in many of these states, it’s not out of the question that former U.N. Ambassador Nikki Haley could pick off a state or two, but barring a massive shocker, the main question tonight is whether she’ll drop out and make Trump the presumptive Republican nominee.

Outside of the presidential race, it’s a day us election nerds have been waiting for — the first day of downballot primary season! We’ve got our eye on dozens of primary contests happening in Alabama, Arkansas, California, North Carolina and Texas, where November’s battle lines will be drawn as we find out which candidates will be on the ballot for everything from congressional seats to city councils.

As always, 538 analysts will be here bringing you the latest results and analysis as polls close, from Vermont and Virginia (7 p.m. Eastern) through Alaska (midnight). Thanks for joining us!

—Tia Yang, 538