Never before has a presidential nomination been determined by a do-over. This year there may be two. And they may not be enough to prevent a bloodbath at the Democratic convention in Denver in August.

Sen. Hillary Rodham Clinton's victories Tuesday in Texas, Ohio and Rhode Island primaries mean the battle for the Democratic nomination will go on and on. But thanks to the Democratic Party's bizarre rules, she didn't gain much ground on Sen. Barack Obama. Despite winning Rhode Island by 18 points, Ohio by 10 points and Texas by 4 points, Mrs. Clinton shaved only about 12 delegates from Mr. Obama's lead, with 10 still to be allocated.

That lead is pretty narrow. According to the Associated Press, Mr. Obama has won 1,360 delegates in primaries and caucuses to date, compared to 1,220 for Mrs. Clinton. Mr. Obama needs 665 more delegates to obtain the 2,025 needed to win the nomination. Mrs. Clinton needs 805. But only 614 delegates are left to be won in the remaining primaries and caucuses, 158 of them in Pennsylvania's primary April 22. That means the nominee will be picked by the 796 unelected superdelegates. (Of these, 208 have declared support for Mr. Obama and 242 for Mrs. Clinton, but they are free to change their minds.)

If the superdelegates retain their current allegiances, and no additional ones declare, Mr. Obama could claim the nomination if he wins 74 percent of the delegates in the remaining primaries and caucuses. Mrs. Clinton would need 92 percent. Thanks to the Democrats' proportional representation rules, the actual split is likely to be close to 50-50, with Mrs. Clinton, because she is currently favored to win in Pennsylvania, winning slightly more than half.

The totals above do not include 210 delegates from Florida and 156 delegates from Michigan because the Democratic National Committee stripped those states of their delegates after they violated party rules by holding their primaries before Feb. 5. The DNC asked the presidential candidates to boycott those primaries. The other candidates obeyed, but after agreeing not to, Hillary Clinton semi-campaigned in the primaries anyway, and won them.

Mrs. Clinton, understandably, wants the Florida and Michigan delegations seated. Even if the delegates she claimed to have won in those states were added to her total, she still would trail Mr. Obama, but the difference would be slight. Mr. Obama, understandably, doesn't want them seated. He obeyed the rules; she didn't, and shouldn't be rewarded for cheating.

The only way the Democrats can avoid a nasty credentials fight is to have a do-over. But what kind? The party would prefer caucuses, because they're cheaper. So would Mr. Obama, because he's done much better in caucuses. But Mrs. Clinton would insist on new primaries.

It would be in the best interest of the Democratic Party to schedule new primaries in Michigan and Florida. Mrs. Clinton cannot overtake Mr. Obama among elected delegates. But she could demonstrate to the superdelegates that he's an empty suit with a glass jaw.

Mr. Obama has risen as high as he has in part because of uncritical coverage by the news media. But that's been changing since his campaign dissimulated about what a senior aide told Canadian officials about the North American Free Trade Agreement; since Antoin Rezko, a major contributor to Sen. Obama, went on trial in Chicago, and since Saturday Night Live lampooned the love affair between the Illinois senator and his traveling press corps.

Mr. Obama bolted from a news conference Tuesday in San Antonio when he was asked hostile questions. He had "the surprised look of a man bitten by his own dog," wrote The Washington Post's Dana Milbank.

Suppose there are some awkward revelations in the Rezko trial and Mrs. Clinton wins Pennsylvania as decisively as she won Ohio. This would put superdelegates in a quandary. Should they go with the guy who was hot in February, or the gal who was hot in March and April?

Reruns in Michigan and Florida could remove doubt. If Mrs. Clinton won them both, then the superdelegates could regard this as proof that the bloom is off the Obama rose. If Mr. Obama won them both, then Mrs. Clinton might yield gracefully, instead of having to be dragged, kicking and screaming, from the race.

But what if Mr. Obama wins in Michigan and Mrs. Clinton wins in Florida? Or vice versa. Then you have a mess only a Republican could love.