During the nomination process political battles are most likely to occur in what forum?

The modern nomination process includes several primary elections and the nomination is usually wrapped up before the convention. The candidates campaign for these elections by making speeches, making statements to the press and sometimes by a debate with the other candidates. Everything they say of note is reported to the nation, so their differences become public knowledge. Of course, if the nomination is still open at the convention, there would be major battles there, mostly behind the scenes.