I'd consider Nixon a rising star, given his quick g to political prominence while and Congress and being picked for VP after with less than 2 years as Senator.
True, but he certainly wasn't a 'rising star' when he was elected, and one could argue that he was a dud as well, considering how his presidency ended.
Which brings up perhaps an important point. Need a rising star still be a rising star when they're elected? When you see Nixon in 1951 and think "that kid's going places", that doesn't mean he need be nearly as exciting once he's actually in a place to go or be at those "places". Barack Obama got into office in a very short timeframe such that there was little transition from "rising star" to President. Is that short timespan absolutely necessary?