Democrat Hillary Rodham Clinton, newly defiant against her own party leaders, sought a victory Sunday in Puerto Rico’s presidential primary that would give her a toehold on an increasingly slippery path to the nomination.

The island territory, once a political asterisk in presidential contests, stood as Clinton’s last best electoral chance. She, former President Clinton and their daughter Chelsea have spent a combined 15 days in the commonwealth hoping to keep her relevant in the contest.

Sunday’s vote follows the decision Saturday by a panel of the Democratic National Committee to give each Michigan and Florida delegate a half vote at this summer’s convention. It was a compromise that did no harm to Obama’s near claim to the nomination but infuriated the Clinton camp and prompted new threats to carry the fight to the August convention.

“This decision violates the bedrock principles of our democracy and our party,” the Clinton campaign said in a joint statement from Harold Ickes and Tina Flournoy, two of her advisers.

The deal by the party’s Rules Committee placed Obama 66 delegates short of the total he needs to clinch the nomination. The election Sunday and two final primaries Tuesday will close that gap, and Obama could attract enough superdelegates to secure the nomination this week.

Clinton campaigned hard in Puerto Rico, spending several hours Saturday on the back of a pickup truck in a salsa-blasting, 40-vehicle caravan through the outskirts of San Juan. In a sign that her supporters were unwilling to give up, an outside group financed by her labor backers bought $150,000 worth of television ads on the island promoting her views.

The group, the American Leadership Project, was also spending $300,000 on ads in Tuesday’s primary states of Montana and South Dakota, states where Obama is deemed the favorite. Clinton planned to campaign in South Dakota Monday.

Saturday’s party meeting did strengthen one of Clinton’s key arguments for staying in the fight. In seating the Michigan and Florida delegates, party leaders tacitly acknowledged her popular vote dominance in those states.

By including the Michigan and Florida results, Clinton can claim to have won the most popular votes since the primaries and caucuses began in January. Both states were punished by the DNC for moving up their contests in violation of party rules and the party had refused to recognize the votes. The candidates did not campaign in either state and Obama withdrew his name from the Michigan ballot.

While polls show her holding a lead in Puerto Rico, officials here don’t expect an exceptionally large turnout. That means Clinton might not get a huge influx of popular votes.