"Hola Puerto Rico!" he shouted to hundreds of cheering islanders - and a few surprised cruise-ship passengers - in Old San Juan. So began that most Puerto Rican of campaign activities: the caminata. Following the speaker truck, and trailed by supporters, Obama strolled the cobblestoned streets of the walled city, shaking hands, signing autographs and pausing every so often to wiggle his hips to the music.
It's presidential politics, island-style - and if it's a departure for the candidates in tomorrow's Democratic primary, it's unlike anything this U.S. territory of 4 million has seen in years.
U.S. citizens since 1917, islanders cannot vote for president. The parties include them in the nomination process, but not since 1980 has a primary race lasted long enough for Puerto Rico's votes to matter.
Hillary Clinton, who is expected to win easily tomorrow, spent several days this week hopping around the island. Obama visited briefly last weekend and is advertising on local radio and television.
At stake in the largest of the three remaining primaries are 55 pledged delegates - more than in Montana and South Dakota combined. Obama, who is closing in on the nomination, will be looking to add to his delegate total. Clinton, who led Obama by double digits in one local poll this week, is hoping to narrow the gap in the overall popular vote.
Where the candidates see voters, Puerto Rico sees an opening. Local leaders, long frustrated by what they view as Washington's indifference, say the primary is a rare opportunity to focus American attention on island issues.
"You know, we're not accustomed to seeing candidates placing ads in papers and the radio and television and making specific commitments," said Roberto Prats Palerm, chairman of the island Democratic Party and co-chairman of the Clinton campaign here. "Puerto Rico has to use this event wisely so that we can generate as much benefit as we can."
For an island with a faltering economy, high crime rates and hundreds of thousands of people without health insurance, that means lobbying for equal participation in federal tax breaks for manufacturing, grants for more police on the streets and programs such as Medicare and Medicaid.
Roberto Padilla, waiting for Clinton to speak in the southern town of Pe?uelas, called the primary "a great opportunity for Puerto Rico's voice to be heard."
"I know that presidential candidates are pretty much informed by their advisers as to the history of the island," said Padilla, an industrial engineer here. "But there's so much to be learned about our culture and our lack of rights. ... We have an extraordinary need of jobs, a great need of infrastructure. We need for us to have an equal opportunity."
Clinton and Obama have been receptive to such calls. But on the central issue here - the island's relationship with the U.S. - they've been careful to avoid taking sides.
Under Puerto Rico's commonwealth status, islanders don't pay U.S. income taxes, but their voice in Washington is limited to a nonvoting delegate in the House of Representatives. Puerto Ricans have long been deadlocked between maintaining that status and seeking statehood, under which they would pay the tax, but also gain two senators, six congressmen and a vote for president.
The bitter debate permeates island politics, hindering progress in education, economic development, law enforcement and other areas. For an American politician to back one option over the other would be to write off the support of half the electorate.
Accordingly, Obama and Clinton have said it's a matter for Puerto Ricans to decide, and they have sought the votes of statehooders and commonwealthers alike.
"All people are entitled to a representative form of government that represents them at all levels of government," Clinton said in Pe?uelas. "I will, as your president, on day one work with all of the factions here in Puerto Rico and with the Congress to enable you to determine your status."
Clinton led Obama by 19 percentage points among Puerto Ricans who said they were certain to vote in the primary, according to a poll released this week by the San Juan newspaper El Vocero and the Univision television network. As a senator from New York, she represents 1 million Puerto Ricans, many of whom have relatives on the island. And she appears to benefit from association with her husband's administration, of which 69 percent of Puerto Ricans expressed approval in the survey by the firm of former Bill Clinton pollster Stanley Greenberg.
Obama appears to suffer from his association with island Gov. Anibal Acevedo Vila, who was indicted by a federal grand jury in March on campaign finance violations. Acevedo Vila, Obama's campaign co-chairman and most prominent supporter, did not appear with him in Old San Juan.
In an island known for high voter turnout, as many as 1 million are expected to vote tomorrow.
"No matter how you look at it, who the president is makes a difference," said Jeff Malley Vega, a corporate attorney in San Juan who backs Obama. "We've paid the price in Iraq, but we had no say in whether we went to war. Helping in any way to determine who's president, even in this half-baked way, is important."
Statehooders hope enthusiasm for the primary will translate into support for their cause.
"If they're showing interest in our issues and they're spending time and money and effort in Puerto Rico now," said Luis Fortu?o, the island's delegate to Congress, "just imagine what would happen if we could vote in the general election."