A few years ago, my husband and I took a houseboat up the Rideux Canal, the waterway that connects Ottawa with Kingston, Ontario.

Houseboats are not glamorous, and the canal is not exciting; it’s a placid waterway that starts in the St. Lawrence River, next to the massive ships from across the world that make the St. Lawrence Seaway, right next to it, bristle with commerce and steel. The ride is a look at the interior of Ontario.

The canal was opened in 1832. It’s connected by a series of locks, huge metal wheels and cogs and levers. That original system still works; the wooden parts have had to be replaced, because they’re constantly in contact with water, but most of the rest of it is original. It’s a marvel of engineering, simple and elegant and remarkably clever.

I’ve been thinking about the canal because I’ve been thinking about the two tunnels that run under the Hudson River, connecting Secaucus and Manhattan’s Penn Station. They were opened in 1908 and they still carry all the train traffic that Amtrak and New Jersey Transit send between New Jersey and New York.

They, too, were impressive feats of engineering, built to last. But not to last this long.

They are in sad shape by now, these tunnels, and the salt water that Hurricane Sandy shoved into them in 2012 has eaten away at their electrical systems and structural integrity. They are dangerous, and they endanger the economy.

The ARC tunnel was a massive project that would have allowed many more trains to go under the river, quickly and safely. Work began on it in 2009, but in 2010, Chris Christie, the Republican governor who apparently thought that the move would endear him to Republicans across the country, but whose presidential ambitions died in the George Washington traffic jam his minions took great glee in creating in 2013, killed it.

The region has suffered. Commuters report more and more time spent in transit as trains are canceled, and officials warn that the tunnels don’t have much life left in them.

The plan is to replace those tunnels with two more through the Gateway Project, another ambitious plan to greatly increase traffic flow under the river. It’s expensive, but according to just about everybody, including the Senate and Congress, it’s necessary, and well worth it.

This is relevant now because last week, Donald J. Trump, who is a native New Yorker but is feuding with the Senate minority leader, New York Democrat Charles Schumer, threatened to pull federal funding from the Gateway project, for no apparent reason other than pique.

Local officials are trying to downplay the threat, hoping that it will go away, but Representative Josh Gottheimer (D-5th Dist.) is clear about the danger that shuttering the project would pose to his district, to New Jersey and New York, to the tristate area, to the Northeast Corridor, and to the country.

“The nerve center of our financial economy runs through this region,” Mr. Gottheimer said. “One-fifth of the American economy depends on the two tunnels that connect the roads from Washington to Boston.

“When you look at our region, which USA Today says generates $1.3 trillion in economic output — that’s 9 percent of the value of all sales and goods and services across the United States,” he continued. “So if that route shuts down, the U.S. economy will lose $100 million a day, according to the Northeast Corridor Commission. (Google the commission to see more astounding facts about the corridor’s importance, and the risks its disruption would cause.)

And then, Mr. Gottheimer continued, beyond the financial costs, there are the human, emotional, and physical ones. “New Jersey is the second state in the nation for people who rely on public transit,” he said.

These are the challenges.

Many commuters take buses to work, of course, and many others drive, but it’s not as if there is a lot of extra capacity to absorb more traffic. The gridlock we see now would be nothing compared to what would happen if a tunnel had to close at rush hour.

“The two tunnels, which are more than 100 years old, are crumbling,” Mr. Gottheimer said. Literally crumbling. If one of them has to shut down, that will paralyze traffic. They close one tunnel every weekend and patch it up. Right now, about 24 trains go through a tunnel at rush hour. On the weekend, it’s only nine. So you can imagine what would happen if we would have to shut one of them down during the week.”

As the tunnels’ ability to handle traffic has decreased, the number of riders has gone up, he added. “Our transit system, New Jersey Transit, has the worst on-time numbers in the country. And between 1976 and 2014, ridership doubled.” That’s a lot more people.

“So in the nerve center of the economy, ridership is up, service is down,” and there are threats not to fix it.

There’s not much local people can do, Mr. Gottheimer said. All the local members of Congress, Democrats and Republicans, are strongly in favor of the Gateway project. But “I think we need to educate people on the impact, writ large, on the country. It’s not just New Jersey and New York.

“It will have a real impact on the entire country.”

I keep thinking back to the idyllic Rideau Canal, still functioning as it was meant to — and probably carrying as much traffic in its entire life as the Hudson River tunnels do in, I don’t know, a day. Maybe two days? Yes, I’m making that figure up, but not the truth behind it.

We can’t rely on quaintness. Our livelihoods, and in fact our lives, depend on our being able to cross the river quickly and safely. That’s a basic government obligation — it’s what we pay our taxes for — and we need it.