The win puts Trump just a few dozen delegates from the 1,237 threshold.
"We're going to get them because he's not going to win," Trump added.
“Even Bill Clinton chose other women, so you should too!” a Trump surrogate told the crowd.
"It was a very unusual political year," he said.
The former GOP rival cited the vacant Supreme Court seat as the reason for his endorsement.
Clinton jokes it's "worth looking into" legislation to prevent Trump from running again.