Republicans are choosing 40 of the 57 Missouri delegates to their national convention and many may not be supporters of Donald Trump even though the businessman won the state's primary in March.

Trump won 37 of Missouri's 52 delegates in the primary and they are bound to vote for him on the first ballot at the GOP's national convention July 18-21 in Cleveland. But if Trump fails to capture the 1,237 votes needed for a first-ballot victory, the Missouri delegates to be chosen Saturday become uncommitted and are free to support another candidate.

In many states so far, supporters of Texas Sen. Ted Cruz have won spots in the national convention as Trump delegates, much to the ire of the New York businessman, who has complained of a "rigged" system.