Arizona, Florida and Illinois took to the polls to weigh in on the race between Joe Biden and Bernie Sanders, while Ohio, whose primary was slated for Tuesday, postponed it at the 11th hour. The three remaining states will hand out more than 11 percent of the total delegates in the entire race.
We're still waiting on the Arizona results, but here's what we learned from what we've seen so far.
1. Sanders' tough math gets a whole lot tougher
The big story of the night is Biden registering a huge rout in Florida - 62 percent to 23 percent, at last count. It wasn't a surprise that he won, but yet again he won by even bigger margins than some polls showed and was able to rack up big-time delegates because of it. The state accounts for about half of delegates available in Tuesday's primaries, and it wasn't at all close.
Following that up with a win in the second-biggest delegate prize of the night, Illinois, puts Biden on course to more than double the 148-delegate lead he came into the night with - despite there being only 441 delegates on offer.
Perhaps this math puts it into perspective. At the start of the night, Biden needed 49 percent of remaining delegates to win the nomination outright, while Sanders needed 55 percent. As of this posting, Biden needs 46 percent of the remaining delegates, while Sanders needs 61 percent.
In other words, the delegate math just got a lot tougher. We knew it would get tougher because these aren't Sanders states, but Biden registered the kind of margins he needs to begin putting this race out of reach.
2. And now the but ...
While Biden's delegate lead is now commanding, it's not clear when he might be able to add to it or truly knock Sanders out of the race. That's because we don't know when the next states will vote
Ohio wasn't the only state to move its primary in recent days; so too have Georgia, which was set to be the only state voting next week, and Louisiana, which moved its April 4 primary into June. Maryland and Kentucky have also moved their primaries, despite them being more than a month away.
The only states remaining states between now and April 28, as it stands, are three April 4 states with very limited delegates in Alaska, Hawaii and Wyoming, and Wisconsin on April 7. Between them, they have just 137 delegates on offer. With Puerto Rico also set to move its March 29 primary, that's the maximum number of delegates that will be available over the next 40 days - and that's if those states actually vote, which seems increasingly unlikely.
Sanders may be down, but he's not technically out, with about half of all the pledged delegates having been handed out. While it's tough to campaign in this environment, it may be tempting for Sanders to stay in the race and see how things shake out in the coming weeks. Biden was threatening to build a truly insurmountable delegate lead in relatively short order, but that might not happen for weeks or months now.
In other words, the coronavirus outbreak doesn't appear to have slowed Biden's momentum at all, but it could prolong the race if Sanders isn't in the mood to concede.
3. Biden's dominance east of the Mississippi
A big reason the delegate math is so difficult is so difficult for Sanders is that he's getting swamped in not just the South but also in the eastern half of the country. And that was the case again Tuesday.
In fact, as results stand, Biden won every county in Florida - just as he has in Alabama, Michigan, Mississippi, Missouri and South Carolina. He also was winning nearly every county in Illinois - just as he has in Arkansas, North Carolina, Tennessee and Virginia.
And that's despite Sanders having won a strong majority of counties in Illinois in 2016, when there was a very close race. The story was very similar in Michigan, which was also very close four years ago but wasn't at all close this time. Those two states epitomize the backsliding of the Sanders campaign, particularly in the Midwest.
The only states east of the Mississippi River where Sanders has won a fair number of counties, in fact, are in the very northeastern part of the country, near his home state of Vermont: Maine, Massachusetts, New Hampshire and the Green Mountain State.
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