One of the worst transportation bottlenecks in the United States is under the Hudson River between New York and New Jersey. It consists of two single-track train tunnels, both over a century old, which are jammed to maximum capacity during rush hour — some 400,000 people pass through the tunnels on an average work day.

They're also both falling apart. They were already ancient when Hurricane Sandy flooded them both with sea water, inundating them with metal- and concrete-chewing salts. New tunnels to allow for an overhaul of the existing ones, greater ease of maintenance, and more throughput to ease "severe capacity constraints" are probably the single most urgent infrastructure project in the United States.

Amtrak, New York, New Jersey, and the federal government had a sketch of plan to fund and start work on the Gateway project, which would have started badly overdue work by 2018 or 2019. But instead of making America's trains great again, President Trump has proposed slashing funds for Amtrak and federal rail subsidies, thus killing the tunnels. It's yet another broken promise from the guy who was supposedly going to spend a trillion dollars on infrastructure.

The Hudson tunnels get such a tremendous volume of traffic because the Northeast Corridor is one of the world's most important mega-cities and economic centers. Stretching from Boston to Washington, D.C., over 50 million people live there, and it produces a fifth of America's economic output. New York is the center of gravity for the whole region, and thus a potential choke point.

And contrary to the popular stereotype of Amtrak as a hapless nonentity, in the Northeast Corridor it is the most important transportation institution. If we take the whole of air and rail passengers together, Amtrak has increased steadily from 20 percent of Boston-New York traffic and 37 percent of D.C.-New York traffic in 2000, to 54 percent and 75 percent respectively as of 2012 — and ridership has only increased since then. Every day over 750,000 people take Amtrak somewhere in the Northeast Corridor. The reason why is obvious: It's cheaper, almost as fast, and, above all, much more convenient than flying.

Engineers say it's just a matter of time before the tunnels begin to fail, and when they do, it will be the mother of all traffic disasters. Since they are only single-track, capacity would be cut by much more than half, as trains would now have to take turns going each way. The regional highways and airports — most of which are already near full capacity already — are not remotely equipped to handle the flood of displaced travelers.

To be fair, Trump isn't the only Republican who has thrown 50 million American citizens under the train, as it were. Chris Christie did it in 2009, when he bogarted some money New Jersey had promised to pay for a previous tunnel replacement plan so he wouldn't have to raise the gas tax.

What makes it all even more frustrating is that the tunnel replacement plan is, as usual for American infrastructure, hideously overpriced. An initial tunnel replacement in 2003 was estimated to cost $3 billion; that has since soared to $25 billion. What's more, the rest of the Northeast Corridor system is badly in need of upgrades and more capacity. And just for the proposed cost of the Gateway tunnels, a country that got good value for money could build new tunnels, upgrade the entire Northeast Corridor to cutting-edge high-speed rail, and build another such line from San Diego to Los Angeles, with some left over. A bit more spending and reform could bring quality service to forgotten cities across the country, where Amtrak service is genuinely lousy.

If there were ever a time for a hard-nosed dealmaker to take a look at America's janky infrastructure spending, and do some negotiating on behalf of the American people to get a better price, this would be it. With a bit of thought and political effort, we could have trains that were at least not an abject national humiliation compared to the Europe-Japan-China standard. Proudly breaking ground on a cheap, efficient new high-speed train would fit perfectly with Trump's self-image as the man who gets big projects done on time, under budget, and properly.

But his budget proposes slashing spending both for Amtrak and federal rail spending. He'd make our already dismal system much worse — and not just in the Northeast Corridor; the cuts also mean completely cutting off passenger rail service to 220 cities.

Trump is a knave and a fraud, in thrall to whatever Heritage intern is writing inexplicable Republican anti-train prejudice into law, who learned all he knows about transportation from looking out the window of his private jet.