But Democrats, hopeful that the Medicare fight is a path to a political turnabout, are clinging to the recent developments like koalas to eucalyptus trees, insisting that the New York race was, as Senator Kirsten E. Gillibrand, Democrat of New York, said, “a bellwether for elections to come.”

It is still a long way to Election Day 2012, the underlying problem of a long-term fiscal imbalance remains as pressing as ever, and Democrats face divisions and message problems of their own. After the Senate vote on the House Republican Medicare plan, the Senate voted 97 to 0 on Wednesday to reject the budget put forward early this year by President Obama, reflecting a recognition by Democrats that they will have to do more than they initially proposed to rein in the expansion of the national debt and address the rising costs of Medicare and other entitlement programs.

But after a 2010 election that seemed to signal not only a Republican resurgence but also a rejection of big government and a need for bold, Tea Party-type steps to slash spending, the politics now look much more complicated. Both parties are being reminded anew that voters like the idea of budget cuts, but that they often recoil when those cuts threaten the programs that touch their lives.

The divisions among Republicans over the Medicare plan are in large part situational.

Three of the Republicans senators who voted against the House plan on Wednesday are moderates from Northeastern states: Scott P. Brown of Massachusetts and Susan Collins and Olympia J. Snowe of Maine. A fourth, Lisa Murkowski of Alaska, won re-election in November as a write-in candidate after being defeated in the Republican primary. The fifth, Rand Paul of Kentucky, voted no on the ground that the House plan, drafted by Representative Paul D. Ryan, the chairman of the Budget Committee, took too long to pay down the national debt.