You dance with the one that brung ya, as the saying goes, but Bill de Blasio sees no reason to embrace the maxim. Bill and Hillary Clinton gave him a vital kick-start in politics and, fittingly, Mr. de Blasio chose the former president to swear him in as New York’s 109th mayor four years ago. Times change. For his second inaugural, on Monday, the Clintons were well in his rearview mirror.

Instead, the swearing-in duties fell to Senator Bernie Sanders of Vermont by way of Brooklyn, who, not coincidentally, was Hillary Clinton’s chief rival for the 2016 Democratic presidential nomination. It was Mr. de Blasio’s way of saying that even a pretense of Clintonian centrism was in disfavor at City Hall and that “a new progressive era,” as he called it in his remarks, ruled the day. Mr. Sanders may not have brung him to the dance, but he now had the mayor’s heart.

What that may mean in terms of policy remains to be seen: How, specifically, will Mr. de Blasio build on the successes of his first term, learn from his mistakes, cope with enduring challenges like homelessness and social inequality, and deal with potential fiscal threats created by a hostile Trump administration? Then again, inaugural speeches are designed for clarion calls, not PowerPoint presentations. There is time for details to emerge.

It was a self-confident mayor who spoke Monday for 13 minutes on the City Hall steps. (It was also a sniffling mayor, plainly as uncomfortable as everyone else in 14-degree weather.) He had reason to feel proud. The old year ended with a murder total under 300, the lowest in many decades. Job totals in the city are at record highs. Construction continues to boom. And not since Edward Koch’s inaugural in 1986 had a Democratic mayor retaken the oath in one of the bluest cities in the land.