So though Obama may agree in theory about the need for cuts, deciding what to cut is certain to be divisive. On the party’s left, many progressives hate the idea of touching Medicare at all. In 2011, after Obama flirted with accepting an increase in the Medicare eligibility age from 65 to 67 in talks with House Speaker John A. Boehner, R-Ohio, labor unions and other progressive groups quickly organized campaigns to denounce the idea.

In the party’s center, pro-business New Democrats worry that without major changes in Medicare, the federal deficit will balloon and the economy will suffer. But they didn’t hear much encouragement from Obama this week.

At his news conference Monday, instead of calling for far-reaching reforms, Obama said merely, “I’m open to making modest adjustments to programs like Medicare.”

And instead of proposing steps toward bipartisan consensus on the issue — the only way to fix Medicare because without it any changes will simply become fodder for election campaign attacks by both sides — Obama took a brass-knuckled swipe at GOP conservatives.

“They are suspicious about government’s commitments … to make sure that seniors have decent healthcare,” the president said. “They have suspicions about Social Security.”

Attacks like that may be great for party unity in the short run. But they’re a distraction from what Obama and his allies should be doing: building support among their own voters for real reform in Medicare, and then working to bring pragmatic Republicans along.

Otherwise, the now-victorious Democrats risk finding themselves, four years from now, in much the same place Republicans are today: so absorbed in maintaining their own unity that they’ve lost voters’ confidence in their ability to govern.