"You don’t come to the convention after you have lost the nomination and not support the nominee," Cornyn said in an interview on Fox News Radio. "I think the right thing to do would be to stay home. I think it was a mistake and I don’t know what it means in terms of his future, but I think he miscalculated."
Cruz, the junior senator from Texas, caused an uproar at the convention last week in Cleveland, where he delivered a primetime speech that offered no support for Trump, his former bitter rival during the primaries. Instead, Cruz urged delegates to vote their conscience in November, prompting an angry reaction from the convention hall as well as from some in the audience at a Texas delegation breakfast the next morning.
The day before Cruz's speech, Cornyn had expressed some hope that Cruz would come around to supporting Trump.
"Obviously with 17 people running for the nomination, there are going to be people who are disappointed, but in all the times I've run for office, I've found there's one irrefutable rule: It's the candidate who gets the most votes wins, and that's just the way it is," Cornyn told reporters after a Texas delegation breakfast. "And so people are going to have their own timetable and their own ways of adjusting to that reality, but I'm looking forward to what Sen. Cruz has to say."
Cornyn and Cruz have not always seen eye to eye. Cornyn has criticized Cruz for using the Senate as a platform to run for president, while Cruz's crusades in Congress have often caused headaches for GOP leadership — including Cornyn, the majority whip.
Madeline Conway contributed to this report.