America’s bridges, roads, and mass-transit systems are not exactly in stellar shape. The American Society of Civil Engineers’ Report Card for America’s Infrastructure—which gave the country an overall grade of “D” in its most recent report—estimates that, in the next five years, the nation’s funding shortfall for rail alone will approach $12 billion.

Unfortunately, things may be about to get even worse. The last congressional bill authorizing funding for so-called “surface transportation” expired in 2009; since then, lawmakers have plugged the gap by passing a series of temporary extensions. Now, Congress has until June 30 to come up with a new bill authorizing funding.

In March, the Senate did just that, approving a measure that extends funding for another two years. The Senate’s bill is far from perfect. It maintains current spending levels at a time when the condition of both our infrastructure and our economy call for vastly more spending. Its provisions on passenger rail fall far short of the aggressive expansion the country needs. But the bill does have one overriding virtue: It passed. And by a wide, bipartisan margin, no less: 74-22. Indeed, the bill has the backing not only of liberal Senator Barbara Boxer (chairperson of the Environment and Public Works Committee) but of her ultra-conservative colleague Senator James Inhofe (the committee’s ranking member). With this kind of pedigree, the bill should have been a no-brainer for the House.

But, rather than embrace the Senate’s legislation, the House GOP responded by pushing its own, utterly unserious bill. Transportation Secretary Ray LaHood, a former Republican member of Congress, has called it “the worst transportation bill I’ve ever seen during thirty-five years of public service.” He wasn’t exaggerating: The House bill slashes funding for Amtrak at a time when rapidly expanding ridership is putting even greater strain on the system’s resources. It exempts many transit projects from the standard environmental-impact analysis, changing the requirements that apply to projects near parks and historical sites and imposing a restrictive deadline on the review process. It tries to raise revenue from controversial oil and gas ventures—including the Keystone XL pipeline.

Perhaps the House bill’s most troubling plank is a proposed reversal of the decades-long practice of setting aside a portion of the gas tax to fund mass transit. If it became law, this change would subject vulnerable but important commuter-transit projects to disruptive annual appropriations fights. It’s hard to imagine any public endeavor more in need of a predictable funding process than mass transit. (It’s a major reason why we support the idea of an infrastructure bank, a proposal that has been championed on our website by New Republic Contributing Editor William Galston.) The House’s bill would, disastrously, lead the country in the opposite direction. Whatever else Democrats concede in this fight, they must stand firm against this change, since it threatens to fundamentally imperil an already weak and underfunded mass-transit system.