This story was written by Avi Zenilman and Ben Smith.
While the two campaigns Tuesday accused one another of trying to steal or suppress votes, experts in election administration are focusing on the old standbys: Faulty machines, questionable voter lists, last-minute litigation.
The likely trouble spots, the experts say, include two familiar election reprobates: Ohio and Florida.
But there are also some new entrants, as the broad new playing field of the 2008 presidential election means more states are competitive, more citizens are participating, and the potential for Election-Day meltdowns like the notorious administrative collapse in Florida in 2000 has increased.
Many pointed, in particular, to Colorado as the possible source of a late night November 4, while others suggested that record turnout in states like Virginia and Georgia could challenge local election officials.
"There's still reason to be concerned in terms of what's going to take place in November," said Kimball Brace, whose firm, Election Data Services, advises local governments on election administration.
Brace cited everything from new machines in Cleveland and South Florida to the rise in absentee voting, many of which are counted by error-prone "optical scan" machines.
"The states that we're keeping an eye on [are] still Florida, but also Ohio, and also Colorado. Those three states are the problem ones from an election administration standpoint," he said.
The location of an Florida-2000-style Election-Day meltdown - with the attendant legal clashes, and lingering doubt - is impossible to predict. Such crises only come about in extremely tight elections, and require the confluence of that close vote with an administrative failure.
But despite eight years of federal and state efforts to create a more standardized, higher-tech national framework for election administration, most state votes will still be administered by county election boards whose competence and equipment vary wildly.
The campaigns, meanwhile, have already begun intense legal skirmishing in states like Ohio and Indiana over a new wave of early voting that began in September.
"In South Florida you've got areas that are going to be on their third separate voting technology in their third consecutive presidential election," said Doug Chapin, the editor of the non-partisan Electionline.org. "Ohio once again is in ground zero for policy changes and litigation."
Colorado, meanwhile, is still reeling from a true Election Day meltdown in 2006, a technical failure in Denver that may have swung at least one close race.
"It's squarely in both campaigns' sights," Chapin said. "They were one of the last states to finish their voter registration list. They had a very bad experience with Election Day voter centers in 2006. Lots of changes, lots."
Many states are taking pressure off their November 4 poll sites with a push for early voting, which has been embraced by both presidential campaigns.
"Mail-in voting helps to relieve a lot of the pressure," said Rich Coolidge, a spokesman for the Colorado secretary of state.
But Chapin said early voting comes with its own concerns: The error rate for optical-scan ballots transported to a central location for counting is sharply higher than those tallied on site, he said.
Florida, the state that has been synonymous with Election Day chaos since the 2000 recount, remains especially troubled despite intense local efforts to remedy its problems. A 2006 congressional election was marred by a dispute concerning more than 18,000 "undervotes" on ballots that registered votes for some offices but not for the congressional race itself. The losing campaign claimed that unusually high number of undervotes was due to a software glitch on "touch-screen" voting machines.
In preparation for the presidential election, 15 Florida counties complied with a new edict to abandon their touch-screen voting machines, and switched to optical scan machines, which leave a physical record of each voter's ballot in case of a recount. But this August in Palm Beach County, a close local primary where 3,400 ballots went uncounted - followed by a series of recounts - led officials to worry and re-test the optical scan voting machines.
"We feel pretty good about the machines," said Jennifer Krell Davis, the communications director for the Florida secretary of state, who said most had had a test-run in this year's presidential primaries.
But just in case, "All of the supervisors have been encouraged to plan as if there is definitely going to be a county-wide recount," she said.
Some observers say that the main problem may simply be delays, and depressed turnout, as voters navigate the new machines.
"To me it's the possibility of the long lines that's the issue," said Susan McManus a political science professor at the University of South Florida in Tampa.
In Ohio, where Democrats continue to complain that a Republican secretary of state tilted the rules toward George W. Bush in 2004, the shoe is now on the other foot. Ohio Democratic Secretary of State Jennifer Brunner's directives on early voting, voter identification, and interpreting voter registration forms have taken fire from Republicans.
"What we're worried about is the registration lists," said Terri Enns, a law professor at Ohio State University.
Ohio courts are currently considering whether Brunner is required to supply lists of questionable registrations to county election boards.
Democrats say the county boards could unfairly remove voters due to technical glitches and similar names; Republicans have charged that people who shouldn't be allowed to vote will.
The result of the wrangling may be more voters casting provisional ballots, which require laborious checking and and time-consuming counting.
"It could mean that we don't know the outcome of Election Day as soon," said Enns.
There have also been machine problems. A glitch in the touch-screen machines used during the primary has meant that Cuyahoga County spent September scrambling to test and ensure that new optical scan ballots work.
A spokesperson for Brunner didn't respond to a call seeking comment on the litigation or the preparations.
The newest state on the list of potential troublespots is shadowed by a disastrous election in Denver two years ago. Denver County responded by scrapping its machines and reverting to old-fashioned paper ballots and printed lists of voters this year, but critics are still worried about the state's capacity to manage the surge of registrations in a closely fought race.
"I'm afraid that there will be problems - so many counties are doing so many different things," said state Senator Ken Gordon, a Democrat whose narrow defeat in the 2006 race for Secretary of State is attributed by some to the chaos in Denver that year.
"We're expecting huge turnout, we have a long ballot - and this is where I think the problem will occur," he said, noting that 18 ballot measures may lead to long voting times and long lines at the polls.
While many counties will allow voters to use paper ballots if lines get long, two key counties in the Denver suburbs don't have that option, Gordon said.
"There will be glitches, but the Secretary has confidence in the state of Colorado and the county clerks who have been working diligently,"said Coolidge, the spokesman for the secretary of state, who said that the fact that 40 percent of voters had requested mail-in ballots would keep lines short on November 4.
Observers of election administration, however, say it's hard to predict where the next perfect electoral storm will land.
New Mexico, for instance, was the site of a long vote count in 2004, and is again hotly contested. Tova Wang, the vice president for research at Common Cause, cited Georgia as a state that might have trouble coping with the 2008 contest, criticizing their voter registration requirements.
A spokesman for the Georgia secretary of state, Matt Carrothers, said his department had encouraged a massive surge in early voting, which will take pressure off the Election Day poll sites. And he said the state and counties had put in "an enormous amount of preparation" for the November 4 vote.
Wang also cited Virginia, which may be a crucial battleground this year, as a potential hot spot. Chris Ashby, a lawyer and longtime observer of Virginia elections, who supports McCain, said the "increased use of touch-screen voting machines" could lead to technical problems. But he said the state had passed a test in the high-turnout Democratic primary.
"It's impossible to make predictions," said Wang. "Probably what's going to happen is what nobody anticipates."
Another risk, said Susan McManus, the Florida professor: Even discussing potential problems could have an impact at the polls.
"What I've heard some people worry about is that too much discussion of a meltdown in Florida before it happens may keep at home the very people we're trying to bring into the system," she said.
By Avi Zenilman,Ben Smith