Congressional Democrats think they saw a rare moment of GOP weakness this past weekend, and they’re hoping to exploit it in the next few weeks, even if they don’t know exactly how they’re going to do it.

House Minority Leader John Boehner may have unwittingly added momentum to the Democrats’ push for an extension of middle-class tax cuts while letting those for the wealthy expire when the Ohio Republican told CBS’ “Face the Nation” Sunday that he would vote for a bill that extended Bush-era tax cuts only for couples making $250,000 or less.

Of course, just as cracks in the GOP’s united front against President Barack Obama’s tax cut plan began to show, Democrats were fracturing as well. Several moderates, nervous about the midterm election outcome, announced they would oppose letting the tax cuts expire on anyone.

Still, Democratic leaders are sensing an opportunity to put Republicans on the defensive and fire up their dispirited base during the debate on the issue. And they think the president’s message offensive last week put them in a good position to do just that, even if they can’t get a bill to Obama’s desk before Nov. 2.

“The events of the last few days have made people … more fearless” when it comes to the tax cut debate, one senior Senate Democratic aide said.

Though aides estimate more than 50 Senate Democrats are on board with Obama’s plan, five Members of the Conference — Sens. Ben Nelson (D-Neb.), Jim Webb (D-Va.), Evan Bayh (D-Ind.), Kent Conrad (D-N.D.), and Joe Lieberman (ID-Conn.) — have said raising taxes, even on the rich, is bad policy during an economic downturn.

House Democrats have to contend with their own endangered Members who want to extend the tax cuts for everyone. They also don’t want to take yet another major vote on a bill that cannot get out of the Senate.

Boehner’s comments over the weekend seemed to give Democratic leaders an opening to bring a middle-class tax cut bill to the floor, perhaps even under suspension of the rules to prevent any Republican attempts to add tax cuts for the wealthy. If they bring a bill to the floor under a rule, Democrats will have to work hard to defeat a Republican motion to recommit extending all of the tax cuts.

Democratic aides said there was a deepening split between Speaker Nancy Pelosi (D-Calif.), who is strongly opposed to extending tax cuts for the wealthy, and moderates in her Caucus who fear Republicans will be able to successfully blame them for raising taxes. A group of moderates is circulating a letter pushing for a one-year extension of the tax cuts for the wealthy as well as permanent middle-class tax relief, an idea that has also been floated by Democratic Congressional Campaign Committee Chairman Chris Van Hollen (Md.).

The moderates’ plan “gets us out of our box,” one senior Democratic aide said. “They can’t hit us on raising taxes, and if we do have a fight on it next year, it will be on much better terms. … It’s a lot easier to have the fight when you are only talking about the rich.”

But the aide said Pelosi has been hell-bent on having a fight on extending only the middle-class tax cuts.

This aide feared that forcing a big fight on taxes — an issue that Republicans have traditionally owned — would backfire on Democrats.

“Democrats lose tax fights,” the aide said.

But many liberals think a compromise that allows even a temporary extension of all the tax cuts would further depress voter turnout among the Democratic base and hand control of one or both chambers to Republicans.

In a Monday statement, Sen. Bernie Sanders (I-Vt.), a self-described Democratic socialist who caucuses with Democrats, blasted Republicans and Lieberman for suggesting that all the tax cuts be extended.

“At a time when this nation has a $13 trillion national debt and a widening gap between the very rich and everyone else, the dumbest thing we could possibly do is to provide hundreds of billions of dollars in tax breaks to some of the wealthiest people in America,” Sanders said.

And he called on his leaders to push the issue without compromise.

“The Democratic leadership has got to stand up to this filibuster no matter how long it takes,” he added.

But some Democrats argued that compromising to accommodate a handful of nervous Democrats in both chambers would likely still end in a Senate filibuster.

“Republicans will find an excuse to not give us a win,” another senior Senate Democratic aide said. Sixty votes are needed to overcome a filibuster; Senate Democrats have only 59 Members caucusing with them.

House Members still expect the Senate to act first on tax cut legislation, but aides said Monday that Senate Majority Leader Harry Reid has yet to come up with a plan for how to proceed. The Nevada Democrat held a conference call over the August break to discuss the agenda, including tax cuts. Today’s regular caucus lunch could provide another forum, but aides cautioned that a decision might not be made until later this week or next week.

Democrats perked up when Boehner seemed to flinch at the notion that he and his party would be accused of “holding middle-class tax relief hostage,” as Obama put it last week.

“If the only option I have is to vote for those at $250,000 and below, of course I’m going to do that,” Boehner said Sunday.

Boehner’s statement has not proved to have long legs. No other House or Senate Republican leader has echoed Boehner. Instead, most put out statements demanding that all of the Bush tax cuts be extended.

Rep. Paul Ryan (R-Wis.), the ranking member of the Budget Committee, told Sean Hannity on his radio show Monday that Republicans should be insisting that the Bush tax cuts are fully extended.

“We don’t want to negotiate down,” he said when asked about Boehner’s remarks.

Senate Republicans continued to insist they have the votes to filibuster any tax cut bill that excludes the wealthy.

“Just before the recess, we had a meeting where we discussed this, and every Republican was absolutely supportive of the idea that there shouldn’t be any increases in taxes,” Minority Whip Jon Kyl (R-Ariz.) said. “Some might think that maybe sometime in the future that might be OK, but certainly not now.”

Jackie Kucinich and David M. Drucker contributed to this report.