Congratulations, Mayor de Blasio â€” what now?

Congratulations, Bill de Blasio — elected Tuesday as New York's 109th mayor by an overwhelming margin.

Say this for de Blasio: He ran and won it his way. Alone among all those who ran this year, he articulated where he wants to take New York. That allowed him to come from behind to defeat his rivals in the Democratic Party, and it saw him triumph in Tuesday's general election.

It also helped that he had a sunny personality and a charismatic family. And his populist, Occupy Wall Street rhetoric obviously appealed to people weary of being told to tighten their belts.

As for Joe Lhota, we congratulate him for forcing into this election debate over the policies that brought about the rebirth of New York under Rudy Giuliani and Mike Bloomberg.

As a novice candidate running in a GOP that suffers from a 6-to-1 voter disadvantage in this city, his campaign was always a long shot, and we'll have more to say soon about what Lhota and the Republicans might have done differently.

But this day belongs to the winner, and so The Post congratulates de Blasio on his big victory. The challenge now goes from electioneering to governing, which we believe poses special challenges to the mayor-elect, given the campaign he ran.

Can de Blasio move New York forward without losing the gains made by his two predecessors? The record of "progressive" big-city government — including pre-Giuliani New York — does not incline to optimism here. We will soon see if it's possible to keep crime low after attacking the cops, reform our public schools while threatening charters and keep this city competitive while increasing its spending and taxes.

Certainly the de Blasio agenda won't face much political opposition. Both the new public advocate, Letitia James, and city comptroller, Scott Stringer, are strong supporters of our next mayor. And the new City Council is even more liberal than the outgoing one.

So full congratulations to the mayor-elect. The Post wishes him the best of luck — we suspect he's going to need it.