Adapting and refining the approach used in earlier work on Senate elections, we simulate the impact of universal turnout on each presidential election from 1992 to 2004 and find little evidence that increased turnout would systematically transform partisan competition or policy outcomes. A state-level analysis of exit polls and the Current Population Survey reveals considerable variability in the gap separating voters and nonvoters. In most cases, nonvoters are just slightly more Democratic than voters. However, a handful of states, such as Texas, consistently feature a large “partisan differential,” in which nonvoters come disproportionately from demographic groups that are more Democratic than voters. We find that universal turnout may well have tipped an extremely close election—such as that of 2000 or even 2004—into the Democratic column. But the partisan differential is generally small enough that universal turnout would only change the outcome of an already close contest rather than leading to a wholesale transformation of competitive dynamics.