WASHINGTON — Senator Clinton wasn’t the only New Yorker working for votes in Puerto Rico over the holiday weekend.

Rep. Anthony Weiner was again by her side, more evidence of a loyalty to the senator that could fuel Mr. Weiner’s own effort to become mayor of New York City.

Mr. Weiner, who narrowly lost the Democratic mayoral primary in 2005, has been making such weekend trips for Mrs. Clinton for months, to Iowa, New Hampshire, Nevada, and plenty of other places far from the five boroughs. Most members of Congress, particularly those running for local office, devote their weekends to home district appearances.

In Mr. Weiner’s case, though, going with Mrs. Clinton to Puerto Rico could pay dividends for him next year when he runs for mayor of New York, which has a large Puerto Rican population. And staying close to Mrs. Clinton even as her White House bid fades could also help the congressman build bonds with national fundraisers and party operatives.

“He’s laying the groundwork for a 2009 mayoral campaign,” a professor of politics at Baruch College, Doug Muzzio, said. “The fact that he is with her at the end makes a difference, when the proverbial rats have jumped the ship or gone into hiding. You get points for standing by your candidate and demonstrating your loyalty, and one would expect that would be reciprocated.”

Aboard the plane, Mr. Weiner said being involved in a “major league” presidential campaign is valuable experience for him, but played down the significance of a single trip to Puerto Rico more than a year before the election.

“It’s really been about Hillary. It hasn’t really been about me,” the Queens lawmaker said.

In Puerto Rico, Mr. Weiner said, whatever politicking he did was in private conversations.

“It’s been mostly meetings and meals with fellow superdelegates,” he said, adding “I’ve been doing some shlepping of bags.”

Of course, politics is only part of the reason he’s still on the campaign trail while many of the senator’s other boosters have grown quiet.

“I’m doing a lot, but it’s largely because I’m dating Huma,” he said.

That would be Huma Abedin, an aide to Clinton who, in political parlance, works as a “body woman” — forever at the candidate’s side, keeping track of her needs as she races through events.

Cupid is no stranger to the campaign trail, but living out of a suitcase can test a couple. “It’s not a great environment to forge a relationship,” he conceded.

Next year’s mayoral race is expected to be crowded; Mayor Bloomberg is barred by term limits from running for a third term.

Other possible contenders on the Democratic side include the city comptroller, William Thompson Jr., the speaker of the City Council, Christine Quinn, and the president of Brooklyn, Marty Markowitz. The police commissioner, Raymond Kelly, is often mentioned as a possible independent candidate.