The second lesson is that presidential support for reform is a necessary, though not a sufficient, condition for success. As John Boehner, the new speaker of the House, said himself on election night, governing from Capitol Hill doesn’t work — the president has to set the agenda.

If Mr. Obama delivers a good-faith proposal for Social Security, for example in this month’s State of the Union address, then by all means Republicans should offer a serious counterproposal and, depending on their differences, negotiate. If he doesn’t, then Republicans should wait on a new president in 2013.

But they should do more than wait: in the event of presidential inaction, reformers should blame Mr. Obama for the lack of progress and work to make entitlements a litmus-test issue in the Republican presidential primaries. The goal should be to nominate someone willing to make a strong case for reducing entitlement growth as part of a larger strategy to restore American prosperity.