De Blasio will not only be closely watched in New York. Being mayor means drawing a national spotlight that most governors will never even experience. His swearing-in means the platform that the left has embraced, even outside the boundaries of the Big Apple, will be put to the test in a major way.

If his agenda proves popular, it will mean good news for the liberal movement more broadly. If not, then it’ll be bad news for liberals — even those who reside outside the five boroughs.

Then there’s also the questions about Democratic unity ahead of 2016. Clinton has never been a liberal favorite. While she is clearly trying to shore up her standing on the left, questions abound about whether she would draw a primary challenger. Even if Clinton doesn’t, she will face questions about enthusiasm on the left should she run for president.

In short, liberals are about to experience a jolt of energy. But the next year could decide whether that momentum is sustainable or not.