Patrick Semansky / AP Zachariah Long, left, and Edward Ritchie protest against a gay marriage bill in February in Annapolis, Md. Thirty-eight states have laws or constitutional amendments banning same-sex marriage. But four states -- Maryland, Maine, Minnesota and Washington -- will vote on this issue, with gay-marriage supporters hoping to net an historic win.

Same-sex marriage advocates have outraised their opponents in many state ballots but have ended up on the losing end in every case.

But this time, their adversaries are worried the large amounts of cash raked in by gay marriage proponents could tilt the balance in high-stakes votes in four states this November.

In Washington, same-sex marriage supporters have raised at least $10.5 million compared with $1.8 million for their opponents. In Maine, they have some $3.35 million as opposed to about $430,000 on the other side, and in Maryland, they have about $3.2 million while the anti-gay marriage camp has more than $835,000, according to public disclosure filings.

“The concern that I have is that the other side will be able to swamp voters with messaging,” said Frank Schubert, campaign manager for the four state campaigns opposed to same-sex marriage.

“I am worried ... about the particular disparities in Maine and Washington state and somewhat in Maryland,” Schubert said. “What’s occurred in the past -- that we’ve been able to win despite being outspent -- you know, is certainly going to be challenged this time by just the sheer disparity that exists.”

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From 2004-2011, all but one of 28 measures to either ban or limit same-sex marriage or partnerships on statewide ballots passed, according to the nonprofit National Institute on Money in State Politics. The one win for same-sex marriage campaigners was in Arizona in 2006 to strike down a constitutional amendment, but their opponents were later victorious at the polls in 2008.

Anti-gay marriage groups were outspent by their opponents in 17 of those contests but won nonetheless, according to Denise Roth Barber, the institute's managing director. “Regarding same-sex marriage, raising more money has thus far not equated to success at the ballot box,” she wrote to NBC News in an email.

Political scientists who conduct research on same-sex marriage votes have reached similar conclusions.

“A money advantage in any race is generally not what it’s blown up to be,” said Patrick Egan, an assistant professor of politics and public policy at New York University whose research includes public opinion on gay rights.

Research shows that a big-money advantage has moved votes by a few percentage points, but those effects tend to die out within a week, he added.

“Gay marriage is an issue on which a lot of people have made up their minds a long time ago and they’re not going to have their minds changed necessarily by a stream of advertisements. You can imagine a number of other kinds of ballot measures that are more confusing or more technical,” Egan said. “Everybody knows exactly what is meant by a ban on marriage or ... approving a law that would allow gay people to get married.”

But the fundraising continues for both sides. Paul Singer, a New York hedge fund titan and Republican, and New York City Mayor Michael Bloomberg, just announced $250,000 contributions each to the campaign to maintain Maryland’s same-sex marriage law passed earlier this year.

Like Maryland, same-sex marriage supporters are asking people in Maine and Washington to vote yes on the ballot, rather than in Minnesota, where they will ask them to oppose a constitutional amendment defining marriage as between a man and a woman (same-sex marriage supporters in Minnesota have raised $5.96 million this year, compared to $1.2 million for their opponents).

A yes vote “requires a heavier lift,” said Fred Sainz, a spokesman for Human Rights Campaign, a national nonprofit backing efforts to legalize same-sex marriage, including financially. “Whenever you’re trying to convince someone to vote yes it’s going to require more resources because the onus is on you to change the status quo.”

That has meant setting up a number of field offices in each state as well as running a ground campaign that involves volunteers going door-to-door to add a personal plea to voters.

Though they have ads and fliers, the personal touch is key to their work, with volunteers in Maine having now spoken to some 200,000 people about the issue since 2009, according to the state campaign. Similar work has been done in Maryland and Washington over the last 18 months, Sainz said.

“Our messaging has changed considerably over the years to now be all about family, love and commitment, and the establishment of a common human bond with the voter,” he said. “Explaining that narrative and that story takes time and money. … It is not a campaign that can be done in two months.”

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The National Organization for Marriage, which opposes same-sex marriage, is running a new fundraising campaign it began two weeks ago that it hopes will net an additional $3 million in the same-sex marriage battle.

“I’ve always said and I continue to believe that really what matters more than what our opponents spend is how much we spend and so my focus has been on working with the campaigns to improve their fundraising across the board so that they have the resources necessary to communicate with voters,” said Schubert, who is also NOM’s political director. “Even though we’re behind, we’re making good progress and I’m hopeful that at the end of the day we will be able to have a strong finish to each of the campaigns to get our messages out.”

Schubert said between 75 to 80 percent of their money will be spent on advertising, noting that they did not have the same infrastructure or staff costs as their opponents since they have a grassroots network through churches they can access.

“Our messaging is just now being delivered … because of the funding disparity,” he said. “I definitely can see a path to victory everywhere. A lot of the path does depend on us being able to raise the resources though … and so, you know, money is not an insignificant factor in a statewide campaign like this."

"I remain optimistic everywhere but that doesn’t mean I don’t have concerns,” he added.

Joel Page / AP Rev. Michael Gray, a United Methodist pastor speaks on Sept. 10, 2012 at a rally outside of City Hall in Portland, Maine, in support of a same-sex marriage.

Kenneth Sherrill, a professor emeritus of political science at Hunter College in New York whose research includes elections and the politics of LGBT rights, questioned if NOM was facing any difficulties.

“They could be playing an expectations game or they could have data," he said. "It may also be that when you’re running a campaign that is appealing to pre-existing prejudices it doesn’t matter if you’re coming in late or if you’re getting outspent. There are certain attitudes that money can’t change.”

NOM’s opponents are also used to them coming out late in the game, such as in California during the battle over Prop 8, a citizen's a ballot measure to ban same-sex marriage that passed in 2008 but was declared unconstitutional on appeal (Schubert led the campaign there, too). That decision was appealed to the Supreme Court, which has not yet said if it will review the case.

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“If you compare their fundraising numbers to our fundraising numbers right now it clearly shows that they are having a cash flow problem,” Sainz said. "What that means to me is that there are very few people that are excited about this issue."

But that does not mean it will stay that way, he said.

“The way in which they do business is that all of their money comes in late,” he added. “We would not be surprised if they flooded, you know, all four … with last minute money.”

Today, 38 states have laws or constitutional amendments banning same-sex marriage, according to the National Conference of State Legislatures.

Polls indicate that same-sex marriage may win this go-around, with a majority supporting keeping such state laws in Washington (56 percent), and Maryland (49 percent), and approving a citizen’s initiative in Maine (57 percent), according to September surveys. However, in Minnesota, 49 percent say they will vote in support of the ban on same-sex marriage, compared with 47 percent opposed.

The importance of these state votes is not lost on either side.

“This November we have one goal in mind and that is to take away the talking point from our opponents that we have never won at the ballot box,” Sainz said.

Schubert said if his opponents netted a win they could use the victory in arguments before the Supreme Court, which is expected to hear same-sex marriage cases during their current term. They may also try to qualify state ballot measures of their own to legalize such unions in other states “that would roll back protections that we’ve already enacted and would open up a whole new front for us to have to fight.”

“There’s a lot riding on what happens here in three weeks,” he said.