New York Gov. Andrew Cuomo (D) undoubtedly wants to run for president in 2020 — but first, he has to be re-elected as governor in 2018.

A year or so ago, he was considered a shoe-in, with his ultra-cynical deception-and-triangulation strategy making him appear above the fray and successfully keeping the left in check. Zephyr Teachout challenged him in the 2014 Democratic primary, and lost by a lot. But the bill is coming due for Cuomo's wretched leadership, and his poll numbers are slipping.

Somebody from the left needs to step up and knock him out of office in the Democratic gubernatorial primary this November.

The biggest problem for Cuomo is the crumbling New York City subway. Years of neglect, incompetence, and austerity (including only partially reversed service cuts from the financial crisis, and the raiding of transit money by Cuomo) have created a service crisis over the last few months. Stations are clogged, people are getting stuck for hours, and the tracks are catching on fire.

With about two-thirds of all New York state residents living in the New York metro area, and 40 percent living in New York City proper, this is a hair-on-fire emergency for the state. It was also one that was easily foreseeable. Gov. Cuomo controls the Metropolitan Transportation Authority, which runs the subway. But instead of doing anything to head off the crisis, he made it worse at every turn.

This is because despite his self-presentation as an effective technocratic manager who "gets things done," Cuomo is staggeringly inept, practically speaking. He's a sort of effective politician, in a vicious and narrowly short-term sense — good at using deceit, betrayal, and conspiracy to gain power for himself. He would have been a passable courtier for Louis XVI.

But only someone who was stupendously ill-informed would let the subway rot as he has. It is the artery system of the state's center of gravity — indeed, the most important city in the country — and without it, New York City could not possibly exist. It turn out that there's more to politics than winning good press and knifing your political opponents at every opportunity.

As a result of his subway bungling, Cuomo's approval rating has fallen by 9 points in two months, to a bare 52 percent. It will probably continue to fall as the reality that the governor controls the subway — and not the mayor, which is commonly believed — sinks in. What's more, there is little reason to suspect he'll be able to sort out the subway problems before the election — infrastructure problems take time to fix, especially in this country, and there's no sign that Cuomo understands how to do it.

With his political stock falling, Cuomo's many enemies are weighing the possibilities. New York Mayor Bill de Blasio would surely like nothing more than to have a genuine liberal who will at least work with him instead of constantly stymieing his every idea out of pure spite. The Working Families Party, which endorsed Cuomo for their ballot line in 2014 on the strength of several promises which Cuomo immediately betrayed, would likely support a credible left-wing challenger as well. And the broader left absolutely despises him.

A primary election would also be a great opportunity to drive home Cuomo's responsibility for keeping Republicans in charge of the New York state Senate, through the "Independent Democratic Caucus," which votes with Republicans. It allows Cuomo to hold the balance of power — and disclaim responsibility for Democratic Party priorities getting repeatedly bottled up in the Senate.

Who will step up? Zephyr Teachout might be game for a rematch; her running mate Tim Wu might be too. There's also perhaps Preet Bharara, the former U.S. attorney recently fired by President Trump. Cuomo is weaker than he looks, and is getting weaker — any credible lefty would have a strong chance of knocking him off in the primary.

If they could pull it off, it will have the salutary effect of knocking Cuomo — one of only a handful of living people who could conceivably lose to Trump — out of the running for the 2020 Democratic primary.

But first, somebody has to step up.