WEST PALM BEACH, Fla. (AP) — Here in a county that knows a thing or two about Election Day meltdowns, both parties are fretting over what might go seriously wrong before, during or just after the Nov. 6 presidential election.

"More than 50 percent of the provisional ballots are thrown in the trash in this state," Florida state Rep. Mark Pafford told about 80 retirees who gathered for last week's meeting of the Golden Lakes Democratic Club.

That's only a slight exaggeration — 48 percent of the provisional ballots cast in Florida in 2008 were rejected. And Pafford's warning underscores anxiety in Florida and other states about legal challenges, ballot problems or bizarre outcomes that could bedevil a race that seems likely to be close — conceivably as close as the 2000 contest that people still quarrel about.

Merely the mention of that election unsettles people in Palm Beach County. The county's poorly designed "butterfly ballot" confused thousands of voters, arguably costing Democrat Al Gore the state, and thereby the presidency.

Gore won the national popular vote by more than a half-million ballots. But George W. Bush became president after the Supreme Court decided, 5-4, to halt further Florida recounts, more than a month after Election Day. Bush carried the state by 537 votes, enough for an Electoral College edge.

"Pregnant chad" entered the political lexicon. And Americans got a jolting reminder of the Founding Fathers' complex recipe for indirectly electing presidents.

Even if everything goes smoothly, it's conceivable the nation will awaken to a major shock in three weeks: an Electoral College tie between President Barack Obama and Republican Mitt Romney. That would throw the decision to the House of Representatives, currently controlled by Republicans but up for grabs in this election.

A 269-269 Electoral College tie is unlikely but far from impossible. It could result, for instance, if Romney wins all the competitive states except Ohio, Wisconsin and New Hampshire.

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Four U.S. elections, including 2000, saw the presidency go to the person who finished second in the popular vote. There has never been an Electoral College tie. However, the U.S. House handed the 1824 election to John Quincy Adams after he finished second — in both the popular vote and the Electoral College vote — in a four-man race in which no one won a majority in either count.

An Electoral College tie isn't the only nightmare scenario that could raise doubts about the election's fairness and worsen partisan bitterness, which already divides Americans and makes compromise in Congress so difficult.

Campaign activists in many states are bracing for possible confusion, delays and even confrontations in polling places on Nov. 6. They are particularly watching Democratic-leaning precincts where Republicans may challenge some people's eligibility to vote.

In recent years, Republican officials in several states have pushed for tighter voter restrictions, including requirements for photo identifications and reductions in the amount of time allowed for early voting. Republicans say they are trying to prevent voter fraud. Democrats, however, note the absence of proven cases of serious election fraud. They say the GOP actions are meant to suppress voting by Democratic-leaning groups such as blacks, Hispanics, low-income people and college students.

Democrats have won court rulings in several states curtailing GOP efforts to shorten early voting periods and require new forms of identification. One Republican initiative that survived, however, is the end to a Florida tradition of allowing voting on the Sunday before Election Day, the "Souls to Polls" day when some black churches would urge congregants to vote upon leaving services.

The Obama campaign has amassed an army of lawyers and non-lawyer volunteers to watch voting places and quickly appeal to state and local election officials if they think legitimate voting is being impeded.

Since 2000, "we've had an amazing group of dedicated lawyers that have been on the ground for 12 years," said Charles Lichtman, a Fort Lauderdale-based attorney helping oversee the Democrats' effort. "So there's nothing they can throw at us that we haven't seen or that we're not ready for."

Other states are doing the same. A single memo seeking lawyers and law students to help safeguard Obama's voter turnout efforts netted nearly 4,000 responses, said Robert Bauer, the campaign's chief lawyer and a former White House counsel.

"The primary issue is making sure the voter experience is secure, fair and reliable," Bauer said.

Romney's campaign also has assembled huge teams of lawyers and volunteers who have spent months getting to know campaign laws and practices in key states, and the election officials who enforce them.

"We have volunteers who will observe the election process at polling places and report potential problems back to our state leadership teams," who in turn will immediately contact election officials, said Romney campaign spokesman Ryan Williams. The campaign "is committed to ensuring a fair and open election," he said.

Some Democrats, however, say they are concerned that GOP voter challenges and procedures at heavily Democratic precincts could create delays, intimidation and lower turnout.

If voters see "a line that's an hour long," they may give up, said Patrick Murphy, the Democrat waging an expensive, high-profile challenge to Rep. Allen West, R-Fla., a tea party favorite. Murphy said a young man said he received a phone call in which someone told him police officers with metal detectors would guard polling places.

Murphy said the man asked him, "Am I going to be arrested?"

Republicans say eligible voters have nothing to fear. But they plan to aggressively watch many Democratic-leaning polling sites.

"I'm almost obsessed" with getting Romney elected, said Kim Bachman, who joined other Republicans to watch last week's vice presidential debate at a West Palm Beach sports bar. The mother of three young sons said she would take a Republican "mini-course" on poll-watching, and spend Nov. 6 wherever the Romney campaign needs her.

One post-election controversy that could inflame tensions and delay an outcome involves provisional ballots, a subject of revised laws in Florida, Virginia and other key states.

Voters cast provisional ballots for numerous reasons: They don't bring proper ID to the polls; they fail to update their voter registration after moving; they try to vote at the wrong precinct, or their right to vote is challenged by someone.

The ballots might eventually be counted, but only if election officials can verify the voters were eligible, which can take days or weeks. Voters cast nearly 2.1 million provisional ballots in the 2008 presidential election. About 69 percent were eventually counted, according to election results compiled by The Associated Press.

In a razor-thin contest, "it's a possibility of a complete meltdown for the election," University of Florida political scientist Daniel Smith said.

The most nightmarish outcomes of all might cause millions of Americans and foreigners to question the fairness of presidential elections. Suppose, for instance, Obama wins more popular votes than Romney, but the two men are tied in the Electoral College. The Constitution gives each state delegation to the U.S. House one vote, meaning a small state such as Idaho has vastly more proportional clout than a big state like California. If the post-2012 House looks like the current one, the Republicans in control would almost surely name Romney president.

It's one thing to have the Supreme Court rule on one state's recount practices, resulting in an Electoral College win for the person who finished second in nationwide ballots. It's another thing to have the sharply partisan House of Representatives break an Electoral College tie in the runner up's favor.

Under another possible scenario, however, it would be Republicans howling in anger. Opinion polls show rising enthusiasm for Romney among GOP voters. That suggests he might run up bigger margins in reliably Republican states, such as Texas and Georgia, than Obama obtains in solidly Democratic states such as California and New York.

Obama might lose the national popular vote but win the Electoral College vote — and thus a second term — by squeaking past Romney in Ohio, Wisconsin and Iowa, while losing Florida and all the other competitive states.

In essence, it would be a partisan reversal of 2000, the year that prompted countless Americans to wish for clean, clear, no-questions-asked election outcomes.

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Follow Charles Babington on Twitter: https://twitter.com/cbabington.