During the 2016 primary, on live television
We cannot allow a con artist to get access to the nuclear codes of the United States of America.
2016 campaign
He called Trump "erratic," "dangerous," and "wholly unprepared," and warned he would "fracture" the Republican Party. "A con artist is about to take over the Republican party and the conservative movement," he said, "and we have to put a stop to it."
Sources: PolitiFact · Reported on the right (Washington Times)
At a rally in Dallas, February 2016
Friends do not let friends vote for con artists.
Dallas, Texas · February 26, 2016
He mocked Trump's business record, read his misspelled tweets aloud to the crowd, and said it was "time to pull off his mask so that people can see what we are dealing with here." He called Trump a con man who "runs on this idea he is fighting for the little guy, but he has spent his entire career sticking it to the little guy."
Sources: The Texas Tribune · The Dallas rally (Texas Tribune)