According to this story, the U.S. Secret Service says the only hotel near the 2016 Republican national convention that is secure enough to house the presumptive Republican presidential nominee is the Inter Continental Hotel, which is on the campus of the Cleveland Clinc. The story further says that the 15th floor has been set aside for the presumptive nominee. UPDATE: see this story from New York Magazine.

Therefore, if no one knows who the presumptive nominee is at the beginning of the convention, that causes a problem.

The story quotes Matt Borges, chair of the Ohio Republican Party, as saying that of course there will be a presumptive nominee. Borges also says not a single vote has yet been cast in any presidential primary. He is incorrect. Absentee voting started in New Hampshire on January 7.