When the Defense Subcommittee of the Senate Appropriations Committee meets to mark up the FY 2015 Pentagon spending bill next week, it has a chance to strike a blow for fiscal discipline and sound national security policy. It can do so by scaling back the troubled F-35 Joint Strike Fighter program.

The recent grounding of the F-35 due to a fire on the runway at Eglin Air Force Base is just the latest in a series of technical problems suffered by the program. These failures don’t come cheap: the F-35 is slated to cost taxpayers up to $1.4 trillion over its lifetime — the most expensive weapons program ever undertaken by the Pentagon.

Issues with the plane have included lags in software development that make it unsuitable for combat; cracks in the engine; and flaws in the million-dollar high-tech helmet that is supposed to tell pilots what is going on around them.

A big part of the problem with the F-35 is the “buy first, fly later” approach to developing it. The Pentagon’s chief weapons buyer, Frank Kendall, has described this approach as “acquisition malpractice,” and promised to do better. But the fire at Eglin is just the latest indication that the program is far from being “back on track.”

The real problem with the F-35 is not how it’s being built; it’s that anyone at the Pentagon thought it would work in the first place. The F-35 was conceived in the 1990s under the name Joint Advanced Strike Technology. The idea was that versions of the plane would be built for the Air Force, the Navy and the Marines, resulting in a large production run that would increase economies of scale and keep costs down.

Past practice should have told the Pentagon that a plane designed to do so many things would be unlikely to be able to do any of them well. In the 1960s the Pentagon devised the F-111, a multi-role fighter-bomber that was supposed to be capable of doing everything from dropping nuclear bombs to flying low to the ground at supersonic speeds. The aircraft had several crashes in Vietnam and it was not used for the bulk of its time in service.

There is a real danger that the F-35 program will go the way of the F-111. Even if all of its current technical problems can be solved, it will too small to serve as an effective bomber, not maneuverable enough for aerial dogfights, and too fast and vulnerable to do well at supporting troops on the ground.

The larger question is what missions the F-35 is meant to fulfill in the first place. It is still unclear why the armed services need more than 2,400 of these planes. The most likely U.S. adversaries in the foreseeable future cannot compete with current generation U.S. aircraft. And it’s hard to imagine a circumstance in which F-35s would be used as fighters or bombers against a nuclear-armed rival like China.

Given all of its problems, why is the F-35 program still alive? It’s mostly due to technological hubris and pork barrel politics. Lockheed Martin and the Air Force continue to assert that the planes can be made to work as advertised. For their part, key legislators like the 49 members of the Congressional Joint Strike Fighter Caucus want to continue a program that creates jobs in their districts — albeit not nearly as many as the company claims.

In fact, a study conducted earlier this year by the Center for International Policy demonstrated that the bulk of F-35 jobs were concentrated in just two states — Texas and California.

Members of Congress who are being lobbied to support the plane based on its economic impacts should take a closer look at whether the program actually supports significant numbers of jobs in their district. In many cases it will not.

The last line of defense for the F-35 is that there is allegedly no alternative. But experts like Thomas Christie, the former head of the Pentagon’s independent testing office, have suggested otherwise. They note that upgraded versions of the F-16 and F-18 fighters and the existing A-10 attack aircraft can easily fill the gap until new, more appropriate and mission-specific aircraft can be developed. The Defense Subcommittee of Senate Appropriations should take a step forward this week by cutting F-35 funding for FY 2015. And congressional leaders from both parties should urge the administration to devise a plan to phase out the program altogether.

William D. Hartung is the director of the Arms and Security Project at the Center for International Policy.