That Obama, who started his Presidency as a true believer, has now given up on the idea that he has any special powers to change the minds of his fiercest critics is probably a good thing. His devotion to post-partisan governance has long fed two mistaken ideas: that the differences between the parties are minor, and that divided government is inherently good for the country.

A fundamental fact of modern political life is that the only way to advance a coherent agenda in Washington is through partisan dominance. When Obama had large Democratic majorities in Congress during his first two years in office, he led one of the most successful legislative periods in modern history. After he lost the House, his agenda froze and the current status quo of serial fiscal crises began. Like it or not, for many years, Washington has been most productive when one party controlled both Congress and the White House.

The boring fact of our system is that congressional math is the best predictor of a President’s success. This idea is not nearly as sexy as the notion that great Presidents are great because they twist arms in backrooms and inspire the American people to rise up and force Congress to bend to their will. But even the Presidents who are remembered for their relentless congressional lobbying and socializing were more often than not successful for more mundane reasons—like arithmetic.