After last week’s primaries, the story was Bernie Sanders’ massive upset in Michigan. Facing a Hillary Clinton victory in a state where he badly needed his message to resonate, he overcame a 20-point deficit in the polls to upend the narrative of the Democratic race. Suddenly, Clinton looked fragile against Sanders’ ability to bring thousands and thousands of young voters and independents to the polls. But missing from most coverage was a simple fact: Yes, Clinton lost Michigan, but she grew her delegate lead that day with a huge win in Mississippi.

We are primed to see national elections as a race for states—if you win the most, you win the election. That’s generally true of the race for president, where electoral votes are winner-take-all, and winning the most states translates to winning the contest. But the presidential nomination is different. It’s a race for delegates under a complex (and often inconsistent) set of rules. And it rewards candidates who can understand and game the playbook to their advantage.

We saw that in the 2008 Democratic primary—not with Clinton but with Barack Obama, who lost large states like Florida, California, and Texas, and either tied or lost the national popular vote (depending on how you count the Michigan primary). But the Obama campaign was less interested in winning states than in maximizing delegates in every contest. Where he had an advantage, Team Obama worked for landslides; where he was losing, Team Obama tried to fight to a draw or modest defeat. The result, after two months of voting, was a structural advantage. Unless Clinton won the lion’s share of delegates going forward (or his campaign imploded under some hypothetical crisis), Obama couldn’t lose.

Which brings us back to 2016. Bernie Sanders has a strong campaign. He’s dominated contests like New Hampshire and kept margins close in states like Massachusetts and Nevada. But Hillary Clinton, having learned lessons from her last campaign, is running a race for delegates. And like Obama before her, she’s run up the score in favorable states and held tight in contested ones. Up until Tuesday’s primaries, this gave her an advantage. And now, with lopsided victories in Florida and North Carolina, she enjoys a structural lead that dwarfs the one Obama held at this point in 2008. Clinton is ahead by more than 300 delegates, which is to say that even if she had lost to Sanders on Tuesday in Ohio, Illinois, and Missouri, her large delegate lead would’ve been safe.

As it stands, Clinton didn’t win only in the South, once considered her sole stronghold in the primary; she captured the Midwest, too, finishing the night with Ohio and Illinois in her corner. (At press time, Missouri was still counting.) With these wins, her delegate lead leaves Sanders in a tight spot even after you bracket “superdelegates” from the equation. Post Tuesday, there are just six states that award more than 100 delegates: California, Maryland, New York, New Jersey, Pennsylvania, and Washington. To win a pledged-delegate lead, Sanders would have to score upset after upset after upset, by unprecedented margins. And that’s with similarly large wins in smaller states. None of this is an impossibility, but I wouldn’t bet on any of it.*

Clinton still has a long slog to the nomination—it takes time to accumulate the delegates she needs—but it’s a clear one, without major obstacles. In a sense, she and her team have reverse-engineered Obama’s 2008 effort, bringing “establishment” resources—huge fundraising and tremendous party support—to bear on an insurgent-style campaign that focused on voter contacts and organizing instead of paid media and massive events. Clinton has made mistakes, and she will continue to make them, but her present campaign is durable enough to survive them.

*This sentence has been updated for clarity.

Read more Slate coverage of the Democratic primary.