Why can't Hillary lock up the nomination?

The realists think Sanders probably can’t win, but plan to vote for him anyway. A CBS poll from April shows that 44 percent of Democratic primary voters want Sanders to win, but only 23 percent actually believe he will win. That suggests at least some people support the senator to indicate political preference, not because they necessarily believe their vote makes it more likely for him to win.

They may recognize that even if Sanders fails to secure the nomination, the more states he wins and votes he amasses, the easier it will be for him to exert influence on the Democratic party platform. They may hope to send a message with their vote, signaling that they don’t support the political status quo. Or they may feel that Clinton is a more viable general election candidate, but simply like Sanders better.

If that’s the case, Clinton’s success may free up even more Democratic primary voters to vote for Sanders without running the risk of jeopardizing Clinton’s shot at the nomination. “For many people, voting is expressive as much as instrumental,” said Kim Nalder, a professor of government at California State University, Sacramento. “They aren’t deluded. They are just more interested in taking the symbolic stand before facing the reality of Clinton vs. Trump.”