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.