Emboldened by a string of casino defeats — including Election Day upsets in East Boston and Palmer — anti-casino activists say they have the momentum to repeal the state’s gambling law as the deadline approaches for organizers to secure nearly 70,000 signatures for a ballot question push.

“The people of East Boston and Palmer really lit a fuse and started this movement. The next few weeks will tell the tale,” said L. Scott Harshbarger, former attorney general and a volunteer adviser with the Repeal the Casino Deal campaign. “It’s still an uphill fight. We’re not taking anything for granted.”

On Tuesday, East Boston voters defeated a proposed Suffolk Downs casino 56 to 43 percent, while Palmer voters rejected Mohegan Sun’s casino bid by fewer than 100 votes. Mohegan Sun is seeking a recount. In September, voters also rejected a Hard Rock casino in West Springfield and Rush Street Gaming dropped its Millbury slots parlor bid under a cloud of resident dissent. A month earlier, Penn National Gaming switched to a slots parlor plan in Plainville after Tewksbury voters rejected it there.

“With the two knockouts in East Boston and Palmer, we’re definitely getting a lot of attention,” said John Ribeiro, chairman of the Repeal the Casino Deal committee. “What we would hear is that it’s a done deal and people maybe thought we would be close, but they certainly thought we wouldn’t win. Now we’re getting congratulated wherever we go. People see me collecting and now they make a point to stop and sign the petition.”

Ribeiro, whose sister, Celeste Myers of No Eastie Casino, led the grass-roots effort against Suffolk Downs, said his group has gone from 125 volunteers to 200 this week and continues to gather support.

“I think momentum is building,” said Republican strategist Brad Marston. “With our improving finances, there will be a lot of pressure and enthusiasm to repeal this thing among various coalitions. I don’t think it would be very difficult to cobble together those coalitions in a statewide election.”

Local elections showed big spending by the casino industry doesn’t win votes, said Marston, who told the Herald if a hard-line progressive, such as U.S. Sen. Elizabeth Warren or another Democratic party powerhouse, were to back the repeal, it could easily catch on.

“But most of their armies and ground troops are unions and unions may be pro-casino for the jobs and the ability to bring those jobs under the union,” said Marston.

Organizers have until Nov. 20 to gather 68,911 signatures to put a ballot question banning casinos in front of voters for the 2014 elections.

Ribeiro won’t say how many signatures they’ve gathered so far, but even if the campaign gets enough signatures, the Supreme Judicial Court must approve the ballot question — the legal aftermath of Attorney General Martha Coakley’s September ruling that it was unconstitutional because it may mean uncompensated taking of property from casino developers.

Harshbarger believes the SJC will side with the campaign because it’s similar to a 2008 ballot question that banned greyhound racing.

“With the greyhound initiative the very same issue was raised and it was upheld by the Supreme Judicial Court. We think that’s the very strong precedent that will carry the day,” said Harshbarger. “Give the people a chance to vote. That’s what people are asking. We’ve never had a vote on this. It was passed by the Legislature.”