Would Pence be the nominee if Trump steps down? Can't they pick Kasich, Ted or Marco?
They can pick anyone they want. The Republican National Committee rules address what would happen should their nominee decide not to or be unable to make it to the General Election on Nov. 8. The issue is addressed in Rule 9 Filling Vacancies in Nominations.
There are two things that can happen:
1. The Party Chair calls a meeting of the National Committee, and the 168-member committee members would vote to fill the vacancy on the ticket. (A candidate must receive a majority of the votes to win the party's nomination.)
2. The RNC can reconvene the national convention for the purpose of filling any such vacancies.
source:
http://www.ajc.com/news/news/national/what-would-happen-if-donald-trump-decided-drop-out/nr86F/However, IMO it would seem like a big slap in the face to Pence.
