WEST PALM BEACH, Fla. – 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.

The mere 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. Four U.S. elections, including 2000, saw the presidency go to the person who finished second in the popular vote.

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 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. There has never been an Electoral College tie.

But that isn’t the only nightmare scenario that could raise doubts about the election’s fairness.

Campaign activists in many states are bracing for possible confusion, delays and even confrontations in polling places 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. 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.

One post-election controversy that could inflame tensions 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.

The ballots might later 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.