Hillary Clinton won Illinois's Democratic primary on Tuesday night, delivering a setback to Bernie Sanders's push to upend the race.
The win caps a great night for Clinton in which she also won Ohio, North Carolina, and Florida — bolstering her delegate total just when Sanders needed to start reducing it. (Missouri still wasn't called at press time.)
Clinton was long considered a heavy favorite in Illinois, where one poll earlier this month put her up by as much as 42 points. But Clinton's polling lead in Illinois shrunk rapidly after Sanders's shocking upset in Michigan — one poll this week put Sanders up by two points — giving Sanders's supporters hope that he could catch lightning twice.
Sanders ultimately came up short. For Clinton, the Illinois victory — coupled with her other wins tonight — should ease jitters that her campaign was on shaky ground.
Illinois was expected to favorable terrain for Clinton
The state was expected to be in Clinton's corner. Exit polls are still coming in, but Illinois will likely have the most black voters of the five states voting today. Clinton was also raised in the suburbs of Chicago, and downstate Illinois looks much like Clinton's stronghold in the South, according to Richard Berg-Andersson, who tracks delegate math at The Green Papers.
There's also the state's strong Democratic establishment, led by Chicago Mayor (and Clinton ally) Rahm Emanuel. "I think that mattered in Massachusetts, and shows why Sanders may not win Illinois," Berg-Andersson said in an interview before the results came in.
In late February, FiveThirtyEight's Nate Silver ran projections for the race to see which states could be expected to "lean" toward one candidate or the other. Silver found that even if Sanders and Clinton were running even nationally, Clinton could be expected to win Illinois by 8 points.
Does this mean we can trust the polls again?
Another reason Clinton may be encouraged by the results from Illinois: they're a sign we may be ready to trust state polling again.
The results from Michigan — which Sanders won after trailing by more than 20 points — had unsettled some experts. It suddenly seemed foolhardy to put too much stock in the other polls — like ones from New York, where Clinton leads by 21 points.
"Who knows what will happen," wrote FiveThirtyEight's Harry Enten in his analysis of the Illinois race.
While the polling from Illinois had gotten closer over the last few days, Clinton's win may shore up faith that her polling leads in other states are meaningful. (Real Clear Politics' average of the Illinois polls had Clinton up by 3 points.) And that should be reassuring for a Clinton campaign that would otherwise be looking at a much more unpredictable primary fight than anyone had expected.