For weeks, Hillary Clinton has looked for the knockout blow that finally forces Bernie Sanders out of the Democratic primary.
She may have gotten it tonight in Kentucky.
Sanders has to start winning every state by a landslide victory to have even a mathematical chance of catching Clinton's nearly 300-delegate lead. Kentucky was called for Clinton as an "apparent winner" at around 9:30 pm by NBC and after 10 pm by Kentucky's secretary of state, who called her the "unofficial winner."
Sanders has maintained that he'll stay in the race until the end of voting, and we don't have any new reason to believe he'll fly the white flag after Clinton's victory tonight. And his hard-line response to the Democratic Party over this weekend's events in Nevada certainly doesn't suggest he's ready to call it quits.
But Sanders needed to win Kentucky to maintain an increasingly far-fetched path to the Democratic nomination. The fact that he lost tonight — albeit by what appears to have been a very small margin — will only dramatically increase the calls for him to exit the race.
Why some observers thought Sanders could win Kentucky
The loss is particularly tough for Sanders's campaign given that Kentucky was one of the more favorable states for him remaining in the race.
"Given the West Virginia results, I think Sanders is probably favored," said Kyle Kondik of the University of Virginia's Center for Politics in an interview Tuesday morning, before voting began. "Sanders has a very good chance in Kentucky."
Sanders will probably face steeper odds in the upcoming contests in California and New Jersey, where have polls have Clinton leading by as much as double digits. Polling from Kentucky was scarce, but the state's largely white and rural voters were widely expected to break for Sanders — as they have throughout the country.
Kentucky has a large number of registered Democrats who are much more conservative than the rest of the party, a group that has in other states backed Sanders in part as a "protest vote" against the party's establishment, according to Kondik.
"More than half of Kentucky’s registered voters are signed up with the Democratic Party, even though the state’s election results have hewed decidedly Republican in recent years," wrote the polling firm Morning Consult in a preview of tonight's contest "That’s an indication of the rightward shift of downscale whites, especially in once union-heavy Coal Country; those are voters who used to call themselves Yellow Dog Democrats."
These voters broke for Sanders by a big margin in West Virginia, and they very well may have in Kentucky as well. But even if they did, it does not appear to have been enough to offset the big difference between Kentucky and West Virginia: diversity.
African-American voters are far more numerous in Kentucky — in part because of its cities, like Louisville and Lexington. (Kentucky's 2008 primary electorate was 9 percent black, compared to just 3 percent in West Virginia.)
Black voters have rescued Clinton's campaign since her first big win in South Carolina in February. And, tonight, they may have helped push her opponent out of the race.
Correction: A previous version of this story incorrectly said Kyle Kondik works for the Center for Responsive Politics, rather than the University of Virginia's Center for Politics.