News that Mayor de Blasio is running for president ignited a lively conversation at a dinner in Manhattan where we found ourselves last evening. The excitement was not so much in respect of Hizzoner’s prospects on the hustings but over who might succeed him to run what’s left of America’s greatest city. The almost unanimous bet turned out to be Congresswoman Alexandria Ocasio-Cortez.

We say “almost unanimous” because we stood pat. It seems to us that Ms. Ocasio-Cortez is having too much fun upstaging her fellow Democrats on the Hill. Why give that up for the chance to feud with Governor Andrew Cuomo and try to run the wreck of the subway system? Any mayor of New York, after all, would have a hard time upending the national news cycle with but a tweet.

Yet the fun Ms. Ocasio-Cortez is having could fade if — as is theoretically possible — the GOP regains the House in 2020. Then she’d be faced with the interminable drudgery of being without seniority and in a minority. One can imagine that the prospect of a mayoral race would look attractive to the young firebrand with a, we don’t mind saying, quick wit and taste for the limelight.

Of course, it was quickly pointed out over dinner, running for mayor wouldn’t be the only option for Ms. Ocasio-Cortez. She could conceivably try to stay relevant by trying to topple Senator Schumer. He is up for re-election at 2022. With passing years, and being trapped in the Senate minority, he has become more and more — to use Robert Musil’s phrase — “a man without qualities.”

The thing that struck us most at the dinner conversation was the unanimity of the view that the Republicans are without prospects in New York. It is a remarkable thing, given that the turnaround of New York City in the 1990s was engineered by, in Rudy Giuliani, a Republican and brought to its apex by, in Mayor Bloomberg at the time, a Republican-of-convenience.

Then again, too, if Ms. Ocasio-Cortez were to run for mayor and the Republicans were to discover a high-spirited millennial with Republican principles to take her on, well, to quote the lottery, you never know. It looks, at least at the moment, like we’re headed for a presidential race in which the front runners in both parties are older than any previous presidents. That can’t last forever.