Puerto Ricans cannot vote for president in US general elections, but their Caribbean archipelago Sunday has a starring role in White House hopeful Hillary Clinton's long-odds comeback bid.
Some 2.4 million electors have a rare chance in the Democratic primary to make their voices heard in top-level US politics, despite having little sway over the federal government that rules them, and no seats in Congress.
The former first lady, bidding to be the first female president of the United States, is hoping for a thumping turnout, to boost her hopes of beating rival Barack Obama in the nationwide popular vote.
"We are depending on the voters of Puerto Rico in our fight to secure the nomination," Clinton said in an email to supporters.
"We have the opportunity to make history in the Puerto Rico primary."
Ahead of a fresh campaign swing through the main island this weekend, Clinton Thursday sprinkled a little showbiz stardust, announcing the endorsement of Puerto Rican Grammy award-winning singer Ricky Martin.
"These elections will have historic repercussions both in the United States and the world. Senator Clinton has always been consistent in her commitment with the needs of the Latino community," Martin said in a statement.
Polling has been sparse on the mainly Spanish-speaking island, and political sentiment is difficult to gauge, but Clinton is tipped to use her hold among Latino voters to take a victory.
Obama has an eye on slicing into the island's 55 elected delegates to the Democratic national convention in August, and has history on his mind, in sight of his goal of being the first black party nominee.
The Illinois senator leads in every key metric of the epic Democratic battle, pledged delegates, top party officials or superdelegates, and nominating contests won.
But Clinton hopes to emerge from Puerto Rico and the last two contests in Montana and South Dakota on Tuesday leading the popular vote, to convince her party that she is the most viable nominee to take on Republican John McCain.
Obama was only 46 delegates short on Thursday of the winning post of 2,026 delegates, according to independent website RealClearPolitics.
The Clinton camp however says that the number needed to grab the nomination is actually 2,210, including delegates stripped from Michigan and Florida, punished for moving their primaries forward into January.
The status of the voided elections is due to be thrashed out by a Democratic Party committee in Washington on Saturday.
The primary, and the unusual presence of big-time American politicians, has sparked some debate about the island's political future.
One major party in Puerto Rico advocates retaining the current relationship with the United States, while another is pushing to become the 51st state. A third, smaller party favors independence.
Both Clinton, and Obama, who has also campaigned on the island, have walked a fine line on constitutional issues -- saying that it is up to Puerto Ricans themselves to decide their status.
Former president Bill Clinton and Obama's wife Michelle have also campaigned on the island, as has former first daughter Chelsea Clinton.
Polls open on Sunday at 8:00 am and close at 3:00 pm (1200 and 1900 GMT).
Puerto Rico is a self-governing commonwealth of the United States under the authority of an elected governor, though its head of state is the US president. The archipelago lies west of the US and British Virgin islands.
Washington controls the island's interstate trade, customs, air and sea space, immigration laws and foreign relations. Puerto Ricans have no voting rights in the House of Representatives or in the US Senate.
The main industries are agriculture, and tourism, and the island is a favorite destination of cruise ships plying the sun-splashed Caribbean.
Landed by Christopher Columbus more than 500 years ago, Puerto Rico was a Spanish colony until it was ceded to the United States along with the Philippines and Guam following the 1898 Spanish-American war.