Mayor Bill de Blasio finally bowed Friday to the unsurprising reality that he got nowhere running for president. 

Rather than prompt more ridicule about the mayor's attempt at alchemy, this could reassure voters that a political tradition can survive in times of tumult.

It remains one of the laws of political gravity that people who run City Hall in Manhattan just don't make it to the White House in Washington. 

Not that it's a big deal, this rule of physics. Mayors of Los Angeles, Chicago, Houston, Miami, Atlanta, Phoenix and San Francisco also don't become president. 

But those other mayors don't occupy the same international media bubble that creates the illusion that if they make it here, they can make it everywhere in the U.S.

Pete Buttigieg remains a declared candidate, but not because the mayoralty of South Bend, Indiana, provides a logical stepping stone.

De Blasio took this leap while still in office. His absence from the city raised serious questions about commitment to his day job.

One big incentive for de Blasio's show of no shame, either before or after his withdrawal, involves term limits. He must leave the mayoralty in 2021 no matter what. City voters won't punish him for the side gig.

Past grabs for the top also proved cringeworthy.

Mayor John Lindsay switched parties from Republican to Democrat to seek the latter party's nomination for president. He quickly flopped.

Nearly four decades later recorded phone calls emerged in which GOP President Richard Nixon snarked about Lindsay, calling the mayor "the new Democrat" and "the convert."

Once, there was even a bit of media buzz about Mayor Ed Koch going for the big prize. He did not.

And it was at this point in the national election cycle in 2007 that former Mayor Rudy Giuliani led in fundraising and polling in the GOP scrum. By the following January, however, the mirage vanished. 

He spent $50 million to win just one delegate.

Mayor Michael Bloomberg's name cropped up for the 2008, 2012, 2016 and 2020 races. Each time his friends and allies pushed the possibility and Bloomberg, who did consider it, declined to make a move.

Real-estate heir Donald Trump's pseudo-populist "real New Yorker" status is another mirage. Sure, he came out of elite Jamaica Estates, before a new wave of immigrants flooded into Queens, but it's not as if anyone would ever run into him on the 'F' train.

As for de Blasio, the Brooklyn Eagle's website headline put the withdrawal in perspective for its local readership: 

"Park Slope Man Drops Out of Presidential Contest."