Single-digit polling of the Massachusetts special election has some Democrats spooked and Republicans salivating at the prospect of 2010 repeat, when Scott Brown exacted an upset Democrats won't long forget — and outside groups on both sides are looking at tipping the scales in their favor with an influx of cash.

Tom Steyer, the California billionaire that spent $630,000 in the primary to back Rep. Edward MarkeyEd MarkeySenators seek to curb counterfeit toys and goods sold online Senate GOP blocks defense bill, throwing it into limbo Equilibrium/Sustainability — Presented by Southern Company — Pledged money not going to Indigenous causes MORE (D-Mass.), looks open to spending in the general election, a source close to Steyer told The Hill.

Steyer's spokesman, Chris LeHane, said that the billionaire is in touch with local climate activists about the race.

"We are in the process of evaluating the race with our local partners, but the more we learn about [Republican nominee Gabriel] Gomez, the more he looks like Mitt Romney without the experience," LeHane said.

SEIU, the union group backing Markey, is thus far the only outside Democratic group to spend in the general election, according to available federal filings. Those filings show that the group has already spent more than $340,000 on the race, largely for "canvassing services" through the June 25 election date.

And the League of Conservation Voters, which has endorsed Markey and spent hundreds of thousands of dollars for him in the primary, expects to continue that level of involvement, spokesman Jeff Gohringer said.

"We made the largest investment by any group in the primary, and we’re going to continue supporting Markey in the general election. This is the biggest race this year for us," Gohringer told The Hill in an email.

Despite tough polling, Markey's still favored to win in June. But Stonehill College political science professor Peter Ubertaccio said the Democratic involvement does reflect "a little bit of concern" about the polls — but more so the haunting memory of 2010.

"I think Markey was prepared to run a very competitive race regardless of the polling. I think Democrats are forever plagued by the Scott Brown election victory, and that they are going to run a very aggressive race regardless of the polls," he said.

Indeed, Markey has already gone on air with two ads of his own, one a negative spot highlighting Gomez's position on gun control.

Ubertaccio added, though, that being in single digits is "not a comfortable zone for Democrats."

Overall, Democratic groups spent more than one million dollars to support Markey in the primary campaign, but they've largely gone silent in recent weeks, waiting, most say, to see where they can be most helpful.

But with Gomez keeping Markey's lead to single digits in nearly every poll of the race, outside Democratic and Republican groups could get much louder in the coming weeks.

The National Republican Senatorial Committee is planning to make a financial investment in Gomez's campaign in the coming weeks, though Republicans won't say what form that investment will take .

And their involvement could open the door to investments from other GOP outside groups.

Asked Monday whether American Crossroads or its affiliated nonprofit, Crossroads GPS, is likely to get involved in Massachusetts, spokesman Jonathan Collegio said the groups are “carefully weighing all the options for engagement there.”

Gomez has found himself on the ropes over the past few weeks due to persistent Democratic attacks on a controversial tax deduction he took in 2005. But an influx of outside spending, most of which would likely be spent to tar Markey, could shift the terrain of the race.

As one national GOP operative put it, outside spending — or the lack thereof — could be a “pivotal factor in the race.”