The US presidential election of 2000 stunned the world by resulting in an effective deadlock that took more than a month - and the Supreme Court - to resolve.
With polls suggesting the US is as evenly divided now as it was four years ago, analysts say this election, too, might end in a virtual draw.
If that happens, the courts may again cast the deciding votes - and both parties are marshalling thousands of lawyers to prepare for the battles that may be on the cards.
Could the election end in a tie?
With something in the order of 110 million ballots expected to be cast, it is unlikely that the popular vote will be an exact tie. However, the Electoral College actually chooses the president, and a tie there is possible.
A Washington Post analysis of 11 swing states found no less than 33 different combinations that would result in a 269-269 Electoral College tie.
Florida has replaced its punch cards with newer machinery
Under the 12th amendment to the US constitution, in case of a tie, the House of Representatives chooses the president. Because Republicans will probably control the House, President Bush would be likely to win.
But the Senate chooses the vice-president, making it theoretically possible that Mr Bush could be saddled with John Edwards as his second-in-command.
The House of Representatives has chosen the president only once since the 12th amendment was adopted. That was John Quincy Adams, in 1824.
Will there be more legal arguments this year?
Probably, given the experience last time round. The Florida crisis of 2000 alerted the public and the parties to the problem of spoiled ballots.
In the past they were not a problem because the majority for the winning candidate was larger than the number of invalid votes.
Now people are much more aware of the issue and if the result is close, more legal disputes can be expected.
Is there a risk of another Florida fiasco?
Probably not in quite the same way.
Last time the biggest problem was with the punch-cards where the pieces to be punched out - the infamous "chads" - did not detach. This time, Florida is using touch-screen voting or optical scanners instead.
However, in Florida and elsewhere there could be legal challenges to the results on several fronts, so further court interventions cannot be ruled out.
What grounds might there be for legal challenges?
There are four general areas of concern.
- The accuracy of voting machines: The new electronic ones have had their trustworthiness questioned and punch-cards, still used in many states, are known to be unreliable.
- Voter registration: Who is entitled to vote and where. This is always a problem in US voting.
- The validity of "provisional ballots" cast by voters who believe themselves eligible, but whose names do not appear on the electoral rolls. Such ballots can be cast this year with verification left until afterwards. But verification can be slow, and what if it is challenged?
- The integrity of absentee voting: Fraud is thought to be easier if voters are not present at the polling stations.
Does the Electoral College system encourage legal challenges?
Yes. Remember that the US president is not chosen by direct popular vote but by an Electoral College in which each state gets a number of votes roughly in proportion to its population.
In all but two states (Maine and Nebraska) the winner of the popular vote wins all the Electoral College votes in that state. This gives candidates a powerful incentive to contest close results.
In 2000, all of Florida's 25 Electoral College votes went to George W Bush although he won by a mere 0.01%. That determined who won the White House.
Are there moves to change the Electoral College system?
Not nationwide, but Colorado is considering a measure to divide its Electoral College votes proportionally instead of giving them all to the winner of the popular vote.
This is called Amendment 36 and it might open up a new legal front. Given the closeness of the race there, the split would probably be five to four in a proportional system. This could decide the presidency in a close race.
The result could be subject to legal challenges over whether such a change can be instituted via a state-wide ballot, and whether it can be made to apply to the 2004 election, as it says it does.
How are challenges made?
In the first instance they go to the local and state authorities who run the ballots. But both state and federal courts can be asked to intervene, on simple procedural grounds or larger constitutional ones.
Strom Thurmond - then 97 - could have become interim president
This happened in 2000. In serious cases, state and federal appeals courts can make rulings. The state supreme courts can also take a case.
In the final analysis it is the US Supreme Court itself which might have to decide an issue and it would normally do so on constitutional grounds.
In 2000, for example, it ruled that hand recounts in Florida would violate the equal treatment clause of the constitution because different voters would be treated differently.
Would another legal row lead to changes in the system?
There would certainly be pressure for a change but the US constitution is written to make change difficult.
The Electoral College has been made much more democratic than it originally was but attempts to abolish it have not succeeded.
The source of the problem in 2000, the physical voting system, is still in the hands of the states and they will not be dictated to, though improvements have been made.
If there is no winner on 2 November, who will run the country in the interim?
Although election day is in early November, a president's term runs from 20 January 2005 until the same date in 2009. That means that President Bush will remain in office for at least two-and-a-half months no matter who wins.
In 2000, the court battles ended well before then, but they went on long enough that serious analysts debated who would take over if there was no result by 20 January 2001.
Bill Clinton could not stay in office due to term limits and his vice-president Al Gore was involved in the dispute.
Dennis Hastert, the speaker of the House of Representatives, was next in line to the presidency, but he would have had to resign his powerful Congressional position and might have preferred not to.
Strom Thurmond, the president pro tempore of the Senate was considered, at 97, too old to be a credible interim president.
Secretary of State Madeleine Albright was ineligible because she was not born in the United States, so conceivably Treasury Secretary Lawrence Summers - fifth in line to the presidency - would have assumed command.