If Trump doesn't win the Republican nomination, does he run a write-in campaign?

[Fuzzy Bear Loves Christian Missionaries]

In many states, in order to vote for a "write-in" Presidential candidate effectively, you have to write in the names of the particular electors you are voting for.  This is an insurmountable barrier to most write-in candidates.  Some states allow for write-in slates, but the slates need petitions to get on the ballot, and that's not easy.