I can see a contested Republican convention happening. Democrats not so much. I think it is unlikely that someone who did not run will be chosen at such a convention, a lot of voters will be put off by the primaries counting for nothing and having had no say in who the candidate is and may stay at home as a result. And I’m not sure everyone will see Trump as an undesirable nominee - he has won a lot of primaries and has a celebrity status straight out of the gate that most candidates can only dream of.