Levitt's 1994 paper on campaign spending employs a unique identification strategy to control for the quality of each candidate (which in previous work had led to an overstatement of the true effect).
The 1996 paper on the median voter theorem develops a methodology for consistently estimating the relative weights in a senator's utility function and casts doubt on the median voter theorem, finding that the senator's own ideology is the primary determinant of roll-call voting patterns.