The biggest worry for this Election Day? Not equipment failure, lousy ballot design or the odd hanging chad, but an ugly brawl over whether minority voters were discouraged from casting ballots, combined with charges of vote fraud.

Over the past two weeks, all the elements of this story have fallen into place. In state after state, Republicans have used one or another variant of the vote fraud charge to claim that Democratic efforts to register supporters and bring them to the polls are tainted by illegality. Democrats have retorted that Republicans are engaged in old-fashioned voter intimidation to hold down minority turnout in close races.

This battle could prove to be far more than a sideshow. The single biggest question in this election is whether Democrats will continue to hold the U.S. Senate. And in one close Senate race after another -- in Arkansas, Missouri, Georgia, South Dakota and North Carolina -- minority voters have the potential to tip the balance.

Thus the nightmare scenario for election night: Imagine excruciatingly close contests in any three of those states. You can expect the Democrats to accuse the Republicans of voter "suppression" and "intimidation." And Republicans to reply by charging the Democrats with "cheating."

I truly hope this doesn't happen, but none of it is fanciful. The charges are already out there.

Take Arkansas, home of the tight Senate race between Republican Sen. Tim Hutchinson and Democrat Mark Pryor. On the first day of early voting in Pine Bluff last week, a group of Republican "poll watchers" showed up with cameras and charged that election officials were not properly checking voter identifications.

Trey Ashcraft, the chairman of both the Jefferson County Democratic Party and the county election commission, accused the Republicans of trying "to intimidate African American voters into not voting." He told the Arkansas Democrat-Gazette: "It's a funny thing they are not stopping whites, only African Americans."

In South Dakota, Democrats organized Indian reservations to add Native Americans to the voter rolls. The goal is to boost Sen. Tim Johnson in his tight race with Republican John Thune. Republicans have touted a handful of cases of questionable or fraudulent registrations to charge that "Tim Johnson and the Democrats are hiding the truth about voter fraud," as the GOP put it in a recent direct mail piece.

The Republican National Committee had to apologize for the mailer over the weekend because it used a headline from a news story that did not even relate to the vote fraud charges. Denouncing what he called "despicable smear tactics," Dan Pfeiffer, Johnson's communications director, told the Sioux Falls Argus Leader that Republicans "want nothing more than to use this issue to suppress the Native American vote."

In Missouri, meanwhile, there is a big fight over whether Republicans will make it difficult for African Americans to cast "provisional ballots" -- ballots held for counting after the election in cases where voter registrations are challenged -- even as Republicans are predicting vote fraud, especially in heavily Democratic St. Louis.

National party leaders already have their talking points. Last week, Senate Democratic leader Tom Daschle declared that the Republican vote fraud charges "appear to be motivated more by partisan politics than a concern with clean elections." Democratic National Chairman Terry McAuliffe called the Republican efforts "reprehensible."

Republican National Chairman Marc Racicot fired back that the Democrats' "racially charged allegations of voter suppression" were an attempt to divert attention from "charges of Democrat vote fraud in South Dakota, Arkansas and elsewhere."

Now, imagine what happens should the Justice Department get involved. The department has announced a national effort to guarantee access to the ballot box and also to ensure voter integrity -- i.e., to fight vote fraud. Wade Henderson, the executive director of the Leadership Conference on Civil Rights, said in an interview that while the Justice Department is "putting a balanced face on its program of voter access and voter integrity," he fears it may be "little more than a warmed-over program of voter intimidation."

Fighting vote fraud is legitimate, Henderson said. But he worries that anti-fraud efforts could overwhelm the goal of guaranteeing minorities access to the ballot.

"What really troubles me," Henderson said, "is that this effort comes on the heels of efforts by Republican committees to pursue their own voter integrity programs."

Perhaps strong words such as Henderson's will have a useful chilling effect on Election Day intimidation efforts and remind Attorney General John Ashcroft's Justice Department of its obligations to fairness. For if election night breaks down into charges of "voter suppression" and "fraud," our democracy will be in even deeper distress than it was after Florida.