He did a lot of sneaky, slimey stuff during the primary when he was running against Trump. That's why he got the name Lyin' Ted.

I'd have to go back and look up a lot of the examples, but I remember he did some sneaky shit to Ben Carson during the Iowa primary, I think, where his campaign announced during voting that Carson was going to drop out or some shit, so that the religious voters would switch their votes to Ted.