METRO’S DEATH spiral cannot be halted without an infusion of money, but politicians in Virginia and Maryland are loath to pump new cash into a transit system that is coming apart. That’s one dilemma. Another is that the requisite qualities for overcoming Metro’s dilemma — bipartisanship, farsightedness and political courage — are as rare as a trouble-free commute on the Orange Line.

Beset by plummeting subway ridership, the system’s $1.8 billion budget faces a $275 million deficit for the fiscal year starting next July. Chances are close to nil that Metro’s three governing jurisdictions — Virginia, Maryland and the District — will tear up their budgets to find that cash in the next few months. That will leave distasteful options, including raising subway fares (for a system whose riders’ patience is already at its limit) and slashing non-rush hour service. Either one would further depress ridership, while buying Metro only a short-term budgetary reprieve.

The threat posed by Metro’s decline to the region’s economic prospects, and to its status as a magnet for young, creative people, is real. The decade-plus of boomtown dynamism cannot be sustained if Metro sinks further into disrepair, and without cash Metro will surely keep sinking.

One year’s deficit can be managed; not so a long-term future of deficits and the shrinking ridership it ensures. Metro, the only major transit system in the United States that lacks a dedicated source of secure annual funding, cannot continue without one.

That’s why Maryland Gov. Larry Hogan’s flat refusal to consider a 1-cent regional sales tax, which would yield $500 million annually earmarked for Metro, is an abdication of leadership. Ditto the reluctance of Virginia Gov. Terry McAuliffe. Mr. Hogan, a Republican facing a legislature dominated by Democrats, and Mr. McAuliffe, a Democrat facing a legislature dominated by Republicans, live in diametrically different political worlds. Yet for different reasons, each is remiss. By contrast, District Mayor Muriel Bowser (D) strongly backs a sales tax for Metro.

Mr. Hogan may fear that backing a levy for Metro would undercut his standing with his base or even invite a primary challenger. He says he will not throw “good money after bad” for Metro. If Mr. Hogan sticks with that position, he fixes his legacy as sealing the doom of the transit system that girds the economic vitality of the nation’s capital. He will be remembered for a dereliction of duty.

Mr. McAuliffe’s excuse — Richmond’s GOP-controlled legislature — is a miscalculation. He sees no hope for success in asking lawmakers to authorize a regional levy for Metro, absent proof that Metro has improved safety and reliability. But whatever strides Metro may make, some Republican lawmakers will deem them insufficient. The way to overcome their opposition is to confront it, as successive Virginia governors did to finally win legislative approval, in 2013, for $6 billion in funding for roads.

Rescuing Metro is a heavy lift, but failing to rescue it will saddle the region with a crushing burden. Starving the system of revenue will not return it to good health.