This year, millions of Americans have voted in congressional primaries and runoffs . These voters, who comprised just 15 percent of the eligible electorate in the last midterm election season, are wasting their time. Thus far, only four incumbents running for re-election this year have lost their primaries, and 121 of those incumbents ran unchallenged. One might assume that incumbents are nearly invincible because they pay attention to their constituents. Even though 8 in 10 Americans are "dis...