The vote of one idiot can cancel out the vote of a single genius — such is the glory of our one-man, one-vote system. But what about the vote of an illegal alien? The deceased? Or a convicted felon? Should they be allowed to spoil the electoral process — and perhaps change history?

And why — in the name of “civil rights” — is Attorney General Eric Holder using the power of the Justice Department to hamstring states trying to put a stop to voter fraud by requiring a secure ID in order to vote?

The answer is clear: In an election that promises to be every bit as close as Bush v. Gore in 2000, each side is going to need every vote it can get. And one way, historically, that Democrats have been able to swing close elections is through fraud. Consider:

* In the 2004 Washington state governor’s race, the Republican’s early lead was overcome by the miraculous discovery of previously uncounted ballots squirreled away in the Democratic stronghold of Seattle, handing the election to the Democrat.

* In the close governor’s race in Connecticut in 2010, a mysterious shortage of ballots in Bridgeport kept the polls open an extra two hours as allegedly blank ballots were photocopied and handed out in the heavily Democratic city. Dannel Malloy defeated Republican Tom Foley by nearly 7,000 votes statewide — but by almost 14,000 votes in Bridgeport.

* Now a new book — “Who’s Counting?” by John Fund and Hans von Spakovsky — charges that Al Franken’s 2008 defeat of incumbent Republican Sen. Norm Coleman may be directly attributable to felons voting illegally.

Coleman led on election night, but a series of recounts lasting eight months eventually gave the seat to the former Saturday Night Live star.

Later, a conservative watchdog group matched criminal records with the voting rolls and discovered that 1,099 felons had illegally cast ballots. State law mandates prosecutions in such cases; 177 have been convicted so far, with 66 more awaiting trial.

Franken’s eventual margin of “victory”? A mere 312 votes.

The Minnesota win gave the Democrats their 60th Senate seat, creating the filibuster-proof majority that helped shovel ObamaCare into law.

Democrats’ chicanery extends back to the days of Tammany Hall and other big-city machines. But today, much of the dirty work is done by lawyers. So maybe it’s not so surprising that Holder is either “investigating” or actually suing states like South Carolina, Texas, Florida and Pennsylvania that have instituted tougher new requirements, including the presentation of government-issued ID.

Never mind that the Supreme Court by a 6-3 vote has already upheld the constitutionality of requiring valid identification in a 2008 case in Indiana.

Holder, the most politicized attorney general since Nixon’s John Mitchell, has consistently moved against any efforts to protect the integrity of the ballot box in the service of the party that keeps him employed.

Infamously, he dropped prosecution of members of the New Black Panther Party, who were intimidating white voters outside a Philadelphia polling place during the 2008 presidential election.

And he killed the case despite the urging of lawyers at Justice and members of the US Civil Rights Commission, which in a 2010 report accused Justice of “open hostility and opposition” to prosecuting cases with white victims.

In a speech last month to the NAACP, the AG charged that Republican efforts to ensure the integrity of the electoral process effectively amount to “voter suppression,” under the absurd premise that minorities are incapable of obtaining proper ID.

Risibly, Holder likened the tougher ID requirements to the days of Jim Crow and the poll tax — despite the fact that, in Pennsylvania for example, the state provides photo IDs free of charge.

Studies show that the cemetery, illegal-immigrant and felon votes tends to break heavily Democratic. Just ask Norm Coleman, who would have blocked ObamaCare and kept circus clown Al Franken away from Washington.