Trump said that once. Have you heard Trump at his rallies and press conferences since then? He addressed it specifically at his press conference following the recent big day of primaries when he was disrupted by protesters. He responded by calmly asking for the people to be removed.
One line is hardly responsible for a well-orchestrated protest in Chicago no less. (Former Chicagoan here, so I know the city and the UIC location well).
I believe it was more than once because I remember other threads not that long ago about Trump wanting to “punch someone in the face” and another time about offering to pay for the legal defense of anyone who “beat the crap out” of his disputers.