Those most affected by the tumult of the recession are also those most likely to have inadvertently fallen off the voting rolls.

Four million Americans have been forced to move by foreclosures. Will they register to vote at their new address? (Reuters)

As the 2000 election showed, a handful of voters can swing the outcome of a presidential contest. That year, just 537 votes in Florida elected George W. Bush president. In 2012, the outcome of the presidential election might come down to another subset of the electorate: the jobless.

I do not mean "the jobless" as a stand in for the struggling economy. I mean actual adult citizens who are out of work. Whether they vote and whether they can vote could be decisive in who wins in November. The latest data shows the U.S. with an 8.1 percent unemployment rate, which translates to 12.5 million people out of work. That understates the number, since it doesn't include at least 844,000 "discouraged workers" who have given up looking for a job.

Even accounting for non-citizens, disenfranchised ex-felons, and 16- and 17-year-olds, there are millions of jobless Americans with the right to vote who may hold the fate of the presidential election in the palm of their hands. The jobless rate has been particularly high in some political swing states. In Florida 8.8 percent of jobseekers are out of work; in Nevada it's 12 percent and in Michigan, 9 percent. That's a lot of potential voters.

Of course, the jobless have a constitutional right to vote. But the recession years have been marked by great upheaval. Some moved in search of work, while roughly 4 million others moved involuntarily due to foreclosures alone since 2007. Even those moving within a city often cross from one voting district into another and inadvertently fall off the voter registration rolls.

As I learned volunteering for an election protection effort, compromising your right to vote is surprisingly easy if you have moved recently.

Part of the problem is that some poll workers -- many of whom are temporary staff who work only on Election Day -- don't understand the laws that apply. Many of the ones I dealt with didn't know the difference between the rules that apply to the presidential race and those that apply for state and local races. Under federal law, if a voter moves across state lines within 30 days of a presidential election, he or she is allowed to vote for president in his or her former state of residence, either in person or by absentee ballot.

The rules are different for state races. Whether a voter can vote in state elections after moving depends on state law. (For a quick snap shot of what rules apply to you, check out the Brennan Center's Guide to Voting After You Move). For most states, voter registration closes approximately 30 days before an election or October 7. Some states provide citizens with a little more time to register. Idaho, Iowa, Maine, Minnesota, Montana, New Hampshire, North Carolina, Wisconsin, and Wyoming all allow voters to register the day of the election. Rules in other states range between extremes. North Dakota doesn't require voters to register at all. Louisianans have to re-register if they move between parishes.

"Motor Voter," the 1993 law requiring that states let driver's license applicants register to vote simultaneously, helps those who change their addresses through the DMV, but the bottom line is voters on the move have to be proactive to protect their franchise. Too often, voters simply forget to update their new addresses with the local board of elections in time.

Many countries have centralized election administration and mandatory voter registration. (Australia even has mandatory voting.) But in the United States, elections are administered locally and the onus is on the voter to register. If she moves, it's her duty to update election officials.

The jobless could hold the keys to the White House if they engage at the ballot box. Just a few hundred jobless voters in a few swing states could make all the difference in this presidential election. But the power to vote hinges on being properly registered. So I hope this can serve as a friendly reminder to those out of work who have moved since last voting: Check to see if you are registered at your current address, and if not, correct it while there is still time. If the voters most affected by the economic collapse are shut out of voting simply because they were displaced from their homes it would be tragic. Fortunately, the tragedy is avoidable.