A resounding defeat Tuesday of a stadium-financing measure by voters in San Diego has those within the NFL wondering if the Chargers will exercise their option to join the Rams in Los Angeles.

It had been widely expected that Measure C would fail to achieve the two-thirds supermajority needed for approval. But after the ballot initiative fell significantly short of reaching even a simple majority, confidence within the league appears to have dimmed that any ongoing attempt by the Chargers to make things work in San Diego would be successful.

“You’d have to think this brings L.A. back into the picture,” one person familiar with the league’s inner workings said Wednesday morning. “That wasn’t even close. Is there a future from them there [in San Diego]? Dean [Spanos, the chairman of the Chargers] will have to figure out what he wants to do. I’m sure that will take a little time.”

The ballot measure reportedly was being supported by about 43 percent of voters, with not all ballots yet counted. It would have raised $1.15 billion in public funding, via an increase in the hotel tax, for a stadium estimated to cost around $1.8 billion.

Spanos, in a letter to fans, said it was unclear at this point what the franchise’s next move will be.

“In terms of what comes next for the Chargers, it’s just too early to give you an answer,” Spanos wrote. “We are going to diligently explore and weigh our options, and do what is needed to maintain our options, but no decision will be announced until after the football season concludes and no decision will be made in haste.”

The Chargers have until Jan. 15 to exercise their option to join the Rams in Los Angeles. The Rams moved from St. Louis to L.A. for this season and are playing at the Los Angeles Memorial Coliseum while their new stadium in Inglewood is under construction.

The option to join the Rams in L.A. would pass to the Oakland Raiders if the Chargers decline it. However, Raiders owner Mark Davis has said he intends to move his franchise to Las Vegas. The Raiders’ relocation would have to be ratified by at least 24 of the 32 NFL owners. The team can apply after the season for relocation. So there will be much for the owners to contemplate in the coming offseason.

“There are some moving parts to this,” the person with knowledge of the situation said.

There is also the possibility that the Chargers could postpone a decision on L.A. The Los Angeles option given to them by the NFL owners contains a provision allowing it to be extended to January 2018. That clause currently is tied to approval of public funding for a stadium in San Diego. But with the Raiders looking to Vegas and the stadium in Inglewood not scheduled to open until the 2019 season, there might not be any need for the Chargers or the NFL to rush.

The Chargers and Raiders had proposed an L.A.-area stadium project in Carson, Calif., but the owners, rejecting a pro-Carson recommendation by their own L.A. committee, chose the Inglewood proposal by Rams owner Stan Kroenke in January, expressing the view that it was more potentially lucrative.

Spanos is said by those within the league to be highly respected by other owners, and the decision to give him the option to join the Rams in Los Angeles probably was largely attributable to the esteem in which he’s held. But there has been ongoing speculation that Spanos and Kroenke are not close and might not be particularly interested in being partners in L.A.

That led, in turn, to a belief among some owners that a narrow defeat in Tuesday’s stadium vote would lead Spanos to keep trying in San Diego. A 50-percent approval rate of the stadium-funding measure could have led to a court challenge in a bid to get the ratification threshold changed. That possibility now dims given the sizable margin of defeat for the measure, and could reduce the Chargers’ options.

Spanos and the Chargers do seem to have repaired their relationship with San Diego’s mayor, Kevin L. Faulconer. The team could attempt to negotiate a new stadium deal with the city or explore other stadium options in San Diego County if Spanos opts against a move to Los Angeles.

“Despite the fact that Measure C failed to receive a two-thirds majority, I wanted to reach out right away with a very sincere thank you for your loyal support as a fan and for considering our initiative,” Spanos wrote in his letter.

“There is much we can be proud of tonight: the 110,000 residents who qualified the measure in just six short weeks; the vocal and passionate support from our fan groups and corporate partners; the strong endorsements and hard work of numerous civic, business, and labor leaders; and the heartfelt efforts of our alumni and players. … The outpouring of support from friends like you, and so many others, has been heartwarming throughout the campaign and I will continue to be mindful of that in the weeks ahead. … Everyone on the team and in my family appreciates your loyal support and continued patience, and we look forward to an exciting rest of the season.”