More than 2 million Democrats in Michigan and Florida cast ballots in presidential primaries held in January, but under party rules their votes didn't count toward picking a nominee.
The issue of what to do about those votes has resurfaced because Barack Obama and Hillary Rodham Clinton are locked in a tight battle for the Democratic nomination.
A look at questions that have been raised:
Q: What's going on?
A: The Democratic National Committee (DNC) stripped Michigan of its 210 delegates and Florida of its 156 delegates to the party's August convention because the states scheduled their primaries before Feb. 5. The candidates promised not to campaign in those two states.
In Michigan, Obama and other Democratic candidates pulled their names from the ballot. Clinton won both primaries, but wasn't awarded any delegates.
Q: Why not allocate delegates based on January voting?
A: Michigan Gov. Jennifer Granholm, a Democrat, and Florida Gov. Charlie Crist, a Republican, have asked the Democratic Party to do that. The Clinton campaign would like the delegates to count. The Obama campaign would not.
DNC Chairman Howard Dean says absolutely not: "We are not going to change the rules in the middle of the game."
Q: What about a second round of voting?
A: Dean says the states can submit plans to hold another round of voting, as long as they comply with party rules. Options include a primary, a caucus, Internet voting (currently used by Democrats who live abroad) or a mail-in vote.
In Florida, Democratic Sen. Bill Nelson said Thursday that there should be another vote, switching from his previous stance that the January results should be used.
Florida House Democratic leader Dan Gelber, who is neutral in the race, has proposed a mail-in vote open to Democrats and independents.
In Michigan, Granholm suggested a "firehouse primary" as long as it is not paid for with taxpayer funds. In a firehouse primary, there are usually fewer polling places and the hours are shorter. Granholm is a Clinton supporter.
Q: How much would a redo cost and who pays?
A: This is the sticky part. Florida spent $29 million on its primary, which included other elections and ballot issues, and Michigan spent $15 million.
Dean says the national party will not pay for more voting. The governors and state legislatures say they won't pay.
The Florida Democratic Party estimates the cost of a mail-in vote at $6 million. Clinton and Obama are both prodigious fundraisers, but they haven't agreed on the need for a do-over or whether they'd pay for it.
Q: If there is a do-over, will the number of delegates needed to win the nomination be increased?
A: Yes. If the Florida and Michigan delegates are added, DNC spokeswoman Stacie Paxton says, a candidate will need 2,208 delegates to win the nomination out of a total of 4,414. It now takes 2,025 delegates to clinch.
Q: How would a redo affect Clinton and Obama?
A: It is unlikely that either candidate can secure the nomination based on voting still to come from 12 remaining nominating contests, in which 611 delegates are at stake. That's because Democrats award delegates proportionally rather than giving all of them to the popular vote winner in a state.
Obama leads with 1,569 delegates and Clinton has 1,462, according to an Associated Press tally. Another round of voting in Florida and Michigan may not put either candidate over the top, but the outcome may provide one candidate with a significant lead. That could be enough to entice "super delegates," the elected officials and party insiders who get to vote for a presidential nominee without being bound by primary results, to flock to one candidate.
Q:Has a do-over ever happened before?
A: Yes. In 2004, the District of Columbia moved its presidential primary to a date before New Hampshire's, against party rules, and the DNC would not allow delegates to be awarded. The district then held caucuses in February to award its delegates.