Early voting is underway, and according to Donald J. Trump, so is voter fraud. Almost daily, he proclaims that “large-scale voter fraud” is happening and that the election is “rigged.” Politicians across the spectrum have criticized this nonsense as divorced from reality, deleterious to our democracy and unprecedented in our elections. It’s good to see such a strong, bipartisan pushback, but the critics are wrong on that last point. Thinly supported allegations of electoral malfeasance have been deployed throughout American history, often by those who want to restrict the vote. In the Jim Crow South, discriminatory devices from poll taxes to all-white primaries were justified as a means of fraud prevention. In 1902, Texas adopted a poll tax. Its champions argued in The Dallas Morning News that the tax would prevent fraud and protect against “corrupt methods at the polls.” Their reasoning? If casting a vote is free, then poor people will sell their votes “for a trifle.” … In itself, there is nothing wrong with poll monitoring. States often allow certified observers to watch polls. Trained poll monitors can help prevent mishaps on Election Day, like ensuring that eligible voters don’t slip through the cracks because of poll-worker error. But undisciplined poll watching can degenerate into voter intimidation.