It's that effective voter manipulation is vastly more effectively accomplished by means *other8 than bussing tens of thousands of bodies (or corpses) to polling booths.

Depress voter turnout, run third-party, identity-appealing, or confusingly-similarly named candidates. Print confusing ballots. Run complex initiatives or propositions with little or no discussion. Leverage majorities in one domain (Senate, statehouses, governor's mansions) to achieve, retain, or negate majorities or minorities elsewhere (vacancies are often filled by gubernatorial or state legislature votes, redistricting is often controlled by statehouse majority, a GoP Senate nullifies much of the power of a Dem House). Have a highly partisan secretary of state certifying statewide elections, including for national office. Have a Supreme Court structure based on few judges, narrow and long-lived partisan majorities, full-bank hearings, and obstructed nominations. Non-trasnsparent, un-auditablre, readily-hacked, and highly partisan technical voting systems. Grossly manipulated media.

Individual voter fraud simply isn't where it's at.