DES MOINES — Republican front-runner Donald Trump has missed crucial deadlines in a number of states to lock up delegates who would stay loyal beyond the first ballot at the party’s national convention in July.

That could doom his presidential candidacy if he is unable to win the nomination in the initial voting at the convention. After the first ballot, most delegates are no longer bound to support the winner of their state’s party primary or caucuses. Instead, they’re free agents who can support the candidate of their choosing.

Most of the delegates are elected at state and congressional district conventions run by party insiders, members of the Republican establishment that Trump has run against from the start of his campaign.

While Trump’s team has had little contact with these loyal party activists, his chief rival for the Republican nomination, Texas Sen. Ted Cruz, has been courting them for months.

Trump has spent the past two days criticizing his party’s delegate selection process as “rigged,” ”unfair” and “corrupt.”

His team is only now starting to engage in the delegate selection process, the choosing of the actual people who will attend and vote at the convention. Republicans have already selected delegates in at least nine states. In others, such as Virginia and Arizona, the deadline to apply to be a delegate has passed.

Indiana’s primary, for example, won’t take place until next month, but the deadline to become a national convention delegate was in mid-March.

“Are we concerned? Yes, definitely,” said Tony Samuel, vice chairman of Trump’s Indiana campaign.

Trump is the only candidate with a realistic path to the 1,237 delegates needed to clinch the nomination before the convention. But the path is narrow, and Cruz is working to block him.

Cruz has built an organization of volunteers who are working in state after state to get his supporters selected as delegates, even those who must vote for Trump at first.

In Virginia, where Trump won the primary, he missed the deadlines to assemble lists of potential delegates. Cruz, however, has delegate candidates in 10 of Virginia’s 11 congressional districts.

Trump’s campaign hired a convention manager, Paul Manafort, last week. Manafort helped lead the fight against Ronald Reagan’s challenge of then-President Gerald Ford at the 1976 Republican convention.

Manafort has accused Cruz’s campaign of strong-arming would-be delegates.

THOMAS BEAUMONT, Associated Press
STEPHEN OHLEMACHER, Associated Press

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Ohlemacher reported from Washington. AP reporters Jonathan Lemire in Albany, New York, Meg Kinnard in Columbia, South Carolina, and Brian Slodysko in Indianapolis contributed.