Representative Nancy Pelosi of California, the Democratic leader in the House, wasted little time on Thursday blasting the Supreme Court’s latest decision freeing donors to spend more money on campaigns. The founding fathers, Ms. Pelosi said at a news conference on Thursday morning, had fought for “a government of the many, not a government of the money.” Democrats, she said, will not “unilaterally disarm.”

Indeed, her fund-raisers had already begun to exploit the new ruling. That morning, Ms. Pelosi’s political team began asking donors for tens of thousands of dollars’ worth of additional contributions permitted by the decision, while circulating a legal memorandum to donors who had questions about the new rules, according to Pelosi supporters.

As constitutional scholars digest the court’s decision, it has already set off a bipartisan scramble for campaign cash, thrusting party leaders, lawmakers with leadership PACs, and candidates into a fierce competition.

The ruling allows donors to make the maximum contribution to an unlimited number of campaigns, freeing donors from caps that required them to pick and prioritize from among each party’s candidates and national committees. And while the decision could inject tens of millions of additional dollars into the 2014 races, it has also left some candidates and party leaders with a new concern: that the biggest donors will get tired of writing new checks.