Taken together, Syria and Summers therefore represent—by history’s decree in the case of military power, and by Obama’s own grandiose vision of the Fed’s role in the economy—the most important second-term presentations of power.

And Senate Democrats were Obama’s undoing in both cases…

This does not mean Obama will lose coming fights over the sequester, shutdown, or debt ceiling. But he is visibly weaker, and even his sense of victory in Syria is so unidimensional, it has no lasting sway in either Democratic cloakroom. More important, Democrats are no longer afraid to defy him or to disregard the will of their constituents—broadly defined in the case of Syria; activist and money-driving in the case of Summers. This, of course, indirectly announces the beginning of the 2016 presidential campaign and an intra-party struggle over the post-Obama Democratic matrix.

This shift—a tectonic one—will give Republicans new opportunities on the fiscal issues and in coming debates over immigration and implementation of Obamacare. Republicans have never known a world where Democratic defections were so unyielding and damaging.