In describing how she would marshal her influence as House minority leader, now and in the coming Congress, Nancy Pelosi has been careful to stipulate that even when Republicans need Democratic votes to pass crucial legislation, Democrats can’t completely thwart the GOP’s ideological aspirations.

“We have leverage if they don’t have the votes,” she told Roll Call earlier this week. “They have leverage because they know we will be responsible. And that allows them to be irresponsible to a certain extent.”

The mismatch here is pretty obvious. Needing votes is a matter of mathematical precision. Deciding what’s responsible and what isn’t is a matter of subjective judgment. A subtext of her comment is that she’s the House Democrat best positioned to make that determination. Three days later, she’s taking her own analysis out of the abstract, and testing critics, who have urged her to relinquish power.

This afternoon, her office has issued at least five urgent press releases, threatening implicitly to pull Democratic support for legislation to fund the government unless Republicans strip a provision from that bill that would allow FDIC-backed financial institutions to trade a wider range of derivatives, weakening the Dodd-Frank financial reform law, which relegated many such trades to uninsured subsidiaries. Translated: if John Boehner and Republicans insist on keeping Wall Street's rider in the bill, they will shut down the government.

This story isn’t as simple as Pelosi vs. Boehner or Democrats taking on Republicans and their Wall Street allies. Plenty of Democrats support weakening rules like this. Plenty of other Democrats were fighting this particular rule before Pelosi got involved. And this isn’t the only contentious rider Republicans have tried to sneak into law, using this month’s government shutdown deadline as leverage.

But Pelosi didn’t sign off on the deal between Republican and Democratic appropriators, which allows her to step in now and exert some of that influence. At the very least, this suggests that some of the goodies Republicans packed into the spending bill will be scrubbed. But I detect greater significance in the fact that she’s using this, of all potential issues, to squeeze Republicans publicly. It says a lot about how Democrats are positioning themselves to magnify the contradictions within the Republican Party from the minority next year.

Outgoing Senate Majority Leader Harry Reid touched on the same idea, in an interview with The New York Times this week.

“Is there enough they can do to help Wall Street? I don’t think so. Big banks? I don’t think so,” Reid said. “That’s where the new battle is going to be.”

Here, in microcosm, is the Democratic old guard making the case that they’re actually best prepared to lead the party in the minority, by showing that Democrats know how to exact a toll when Republicans use their power to advance unpopular aspects of their agenda quietly.