Rubio won't release delegates to remaining GOP candidates

In fact, Rubio sent a letter to 21 states and territories where he was awarded a total of 172 delegates, telling the GOP parties there not to release the delegate votes that he acquired.

In most campaigns, when a candidate drops out, he or she "releases" the delegates to support the remaining candidate of his or her choice at the party's convention.

But Rubio has requested that his name appear on the first ballot at the National Republican Convention in Cleveland, Ohio, in July.

"It is my desire at this time that the delegates allocated to me by your rules remain bound to vote for me on at least the first nominating ballot at the National (Republican) Convention," he wrote in the letter to the chairmen of the states' Republican parties.

"Most states are leaning towards giving him his delegates," said Peter Goldberg, chairman of the Alaska Republican Party. Rubio won five delegates in Alaska, where his request was granted.

>>How many delegates does Donald Trump have?

Rubio's request is likely a move to prevent GOP front-runner Donald Trump from receiving more votes from delegates.