Who said it was unauthorized? Rubio is not in my top three choices, and I could see where some could be made that included both personal and party related at the same time. If he was at a meeting over a few days time and decided to take his family out to dinner or other meals, it would be awkward to ask for separate checks.
It wouldn’t be awkward to ask for separate checks. We go out with friends to restaurants about every other week, and we always get separate checks.