Update: We've compiled reports that offer a look at how Election Day has gone thus far.
Nov. 6: This post has been corrected.
Get ready. Here are all the things that could go wrong (or already have) as Americans head to the polls.
1. Confusion over voter-ID laws spurred by ongoing ads, litigation and misinformation
Despite a state judge's Oct. 2 ruling that Pennsylvania voters are not required to show photo ID this election, the state is continuing with a $5 million ad campaign to broadcast the future requirement: "Show It," the ad slogan reads, with the words, "if you have it," in fine print. (Here's our guide on everything you need to know about voter ID laws.)
A spokesman for the secretary of state told the Washington Post these ads remain "faithful" to the judge's ruling, which held that elections officials could still ask voters for identification, just not require it.
In addition, the state's largest utility company, Peco, sent a courtesy newsletter out to 1.3 million customers in seven counties informing them they'd need valid photo ID to vote — though by that time the judge had already ruled they don't have to.
In Missouri, the Republican candidate for secretary of state is running on a platform favoring a new voter ID law. Because the state doesn't currently have a photo ID requirement — since the courts struck it down — the outgoing secretary of state has said the campaign focus on photo ID is potentially confusing for voters.
In Tennessee, where a voter ID law went into effect this year, state officials were instructing some counties not to honor photo library cards as an acceptable form of voter ID. The city of Memphis sued, and just last week, the Tennessee Supreme Court issued the final word: It affirmed a lower court's ruling that voters can cast regular ballots using free library cards.
2. Disruptions caused by Hurricane Sandy — not just in the Northeast
The destruction caused by the storm is expected to disrupt voting somewhat in solidly Democratic New York and New Jersey, but there are indications it is also causing complications for absentee voting in at least one presidential swing state.
Priya Sanghvi, a 28-year-old filmmaker from Arlington County, Va., requested an absentee ballot on time but didn't get mail at her apartment in downtown New York City all last week. Some mail arrived on Saturday and Monday, but the absentee ballot wasn't there.
When Sanghvi called the Arlington County registrar, who confirmed that her ballot had been sent out, and Virginia's Board of Elections, officials told her their hands were tied: The deadline for returning mailed absentee ballots was 7 p.m. on Election Day.
"I'm at a loss," Sanghvi told ProPublica. "I would literally have to get to Virginia to vote, which I'm not going to be able to do."
It's not clear how widespread absentee voting problems related to disruptions in postal service may be.
"We don't keep statistics on the possible number of ballots that could be delayed due to Hurricane Sandy," U.S. Postal Service spokesperson Darleen Reid told ProPublica in an email. "There is no way to determine this at this time."
Arlington County Registrar Linda Lindberg told ProPublica her office had gotten "a few" calls from people whose absentee voting had been disrupted by the storm, including a voter sent to New York as part of the relief effort.
3. Frustration over shortened early voting in Florida has led to lawsuits
In Florida, the Republican-controlled legislature shortened the early voting time frame this year from 14 to eight days — excluding the Sunday before Election Day. The tighter window has resulted in long lines, frustration and litigation. (As we've also noted, Florida also has among the most confusing ballots in the country — and it's really long.)
The Florida Democratic Party filed a federal lawsuit Sunday to compel the state to extend early voting hours — or to at least allow voters in Miami-Dade, Broward and Palm Beach counties to cast absentee ballots in person on Monday.
Long wait times prompted the League of Women Voters and the Florida Democratic Party last week to call for Florida Gov. Rick Scott to extend early voting hours in the state. Gov. Scott has refused that request.
4. Newly drawn districts may cause some voters to head to the wrong precinct
In South Carolina, according to the Spartanburg Herald Journal, up to "tens of thousands voters statewide" may have been issued absentee ballots that don't correspond to their correct district. If a voter turns in an incorrect absentee ballot, he can't vote again using a correct ballot, according to state elections officials.
5. Provisional ballots could be crucial — and take a really long time to count
In swing states such as Virginia and Ohio, provisional ballots could be the deciding factor — in 2008, more provisional ballots were cast in Ohio than in any other state besides California.
If a voter in Ohio applies for an absentee ballot, disregards it and shows up to vote on Election Day, the voter can only cast a provisional ballot, which won't be counted until 11 days after Nov. 6. More on this can be found here.
In addition, Ohio Secretary of State Jon Husted has ordered county elections boards to reject provisional ballots where a voter doesn't correctly list their ID information. (Ohio law states election officials are supposed to be the ones ensuring the correct information.) Voter advocacy groups have protested the order. A federal judge is expected to rule on the motion by Nov. 17, the first day provisional ballots will be counted in Ohio.
In Virginia, which has an ID law, many voters may be handed such provisional ballots if they can't initially provide an acceptable form of ID.
6. Voter suppression via deceptive mailers, intimidating phone calls
Registered voters in Florida, Virginia and Indiana have received calls from phony elections officials encouraging them to "vote by phone." The complaints have been reported by both Democrats and Republicans.
Voters in at least 23 Florida counties also received letters on "official-looking election office letterhead" questioning their citizenship and voter eligibility. The mailers, which have also apparently targeted both Republicans and Democrats, have sparked an FBI investigation.
One liberal organization recorded a Republican state party member instructing volunteer poll monitors in New Mexico to demand that voters produce ID and to prevent voters from requesting interpreters.
Some pamphlets in Maricopa County, Ariz., incorrectly listed Election Day as Nov. 8 on the Spanish language side of the ballot, even though the correct Nov. 6 date was printed on the English language side.
7. A tie in the Electoral College
If President Obama and Romney each receive the same number of electoral votes, the House decides the presidency and the Senate the vice-presidency.
In the event of an Electoral College tie, the New York Times reports, "strategists envision an intense postelection campaign of state-by-state recounts, lawsuits, qualification challenges, efforts to flip electors, horse trading and pressure on members of Congress," resulting in "a highly volatile 11-week obstacle course to Inauguration Day."
And of course, there doesn't need to be a tie for there to be recount chaos.
ProPublica's Justin Elliott contributed reporting to this story.
Correction (11/6): An earlier version of this piece incorrectly stated that Virginia had a photo ID law. Virginia voters do have to show ID, but not all the acceptable forms are photo IDs.