By Chris Cillizza – washingtonpost.com staff writer

Sen. Hillary Rodham Clinton claimed a convincing win over Sen. Barack Obama (Ill.) in today’s Puerto Rico primary, a victory that may well be her last in her fading bid for the Democratic presidential nomination.

Polls closed in Puerto Rico at 3 p.m. Eastern time and the race was called for Clinton almost immediately by the major television networks and the Associated Press.

For Clinton, the win provides a quick bounce-back from her campaign’s resounding setback on Saturday at the hands of the Democratic National Committee’s Rules and Bylaws Committee, which ruled in Obama’s favor in a dispute over the seating of the Florida and Michigan delegations, but does little to change the overarching dynamic of the primary fight.

While Clinton will win a clear majority of Puerto Rico’s 55 delegates, she will still stand well behind Obama in the overall count. Coming into today’s vote, Obama had 2,052 delegates, 66 short of clinching the nomination. Clinton had a total of 1,877 delegates.

Clinton launched new ads in South Dakota and Montana on Sunday asserting that she is the popular vote leader, securing more votes than any previous primary candidate. “Some say there isn’t a single reason for Hillary to be the Democratic nominee,” says the ad’s narrator. “They’re right. There are over 17 million of them.”

Bill Burton, a spokesman for the Obama campaign, responded by noting that “both Barack Obama and Hillary Clinton have gotten more votes than any presidential campaign in primary history”, adding: “We are, however, ahead in the popular vote now and will be ahead when all of the votes are counted Tuesday.”

According to Real Clear Politics, Obama actually has 166,186 vote lead over Clinton in the popular vote — 17,267,658 to 17,101,472. If Michigan’s primary is included, where Clinton received 328,307 votes and Obama none due to the fact he removed his name from the ballot, Clinton takes a 162,123 vote lead.

The popular vote debate is largely a semantic and symbolic one at this point, however, as the nominee for the party is selected by delegates and Obama appears to be all-but-certain to reach the magic number of 2,118 sometime soon after Tuesday’s primaries in South Dakota and Montana.

Clinton’s last, best hope to reverse that math came and went yesterday when the Rules and Bylaws Committee met to resolve the fate of Florida and Michigan whose delegates were stripped by the DNC after moving their respective primaries too early in the nominating calendar.

The committee granted Clinton less than half the delegates she had hoped to claim from the two states, which were sanctioned by the DNC for moving their primaries up too early in the year in the nomination fight.

The committee’s decision — particularly with regards to Michigan — was met with derision in the Clinton campaign, which floated the possibility of taking the fight over the Wolverine State to the party’s national convention in late August. “We reserve the right to challenge this decision before the Credentials Committee and appeal for a fair allocation of Michigan’s delegates that actually reflect the votes as they were cast,” the campaign said in a statement released immediately following Saturday’s proceedings.

Nonetheless, the committee’s decision to seat the Florida and Michigan delegations at the convention, but grant each delegate only half a vote, resolves a major piece of the nomination puzzle in Obama’s favor.

Puerto Rico was the largest delegate prize left on the board, South Dakota, with 15 delegates, and Montana, with 16 delegates, will bring the 2008 presidential primary process to a close on Tuesday. Even the most ardent Clinton backers acknowledge that their candidate’s pledged delegate deficit will stand in triple digits when all votes are counted on Tuesday

Polling in Puerto Rico, albeit limited, suggested that Clinton was headed for a significant victory. A survey done by Greenberg Quinlan Rosner Research, a Democratic firm, showed Clinton with 59 percent of the vote to Obama’s 40 percent.

Clinton’s demonstrated strength among Hispanic voters during the primary process and her popularity among the large Puerto Rican community in New York (more than one million residents, according to the 2000 Census) combined to give the Empire State senator a significant leg up.

Clinton also lavished Puerto Rico with attention. She and her husband, former president Bill Clinton, and the couple’s daughter Chelsea spent 14 combined days there of late. Hillary Clinton spent Saturday touring local communities on the back of a flatbed truck. Today she made stops in and around San Juan, the country’s capital city.

“Campaigning in Puerto Rico is like one long Puerto Rican Day Parade,” Clinton said on Saturday, in a reference to the annual celebration in New York City. “It is incredibly energizing, exciting.”

Obama devoted far less time to Puerto Rico. His most recent campaign visit was last weekend, and he spent Sunday campaigning in South Dakota. The Illinois Senator will travel to Michigan and Minnesota — two key general election battlegrounds — in the early part of this coming week.

Election officials were preparing for lower-than-average turnout, estimating that a quarter or fewer of the island’s 2.3 million registered voters would go to the polls. There are no local candidates or initiatives on the ballot, and the battle between Clinton and Obama appears all but over.

Washington Post staff writers Anne E. Kornblut and Shailagh Murray contributed to this report