Congressional Democrats succeeded this week in crippling a school choice program operating in the nation’s capital. For the last five years, the D.C. Opportunity Scholarships have made private schooling affordable to 1,700 poor children. Rather than reauthorizing the program for another five-year term, Democrats have all but ensured it will die after next year.

House Appropriations Committee Chairman David R. Obey, Wisconsin Democrat, has asked D.C. Public Schools Chancellor Michelle Rhee to prepare for the return of voucher students to the city’s broken public schools.

Sen. Ted Kennedy’s office claims the senator opposed the voucher program from the start because it “takes funds from very needy public schools to send students to unaccountable private schools.” (The House Budget Committee holds hearings today on the U.S. Education Department budget).

But just how needy are D.C. public schools? To find out, I added up all the K‑12-related expenditures in the current D.C. budget, excluding preschool, higher-education and charter school items. The total comes to $1.29 billion. Divide that by the official enrollment count of 48,646 students, and it yields a total per-pupil spending figure of $26,555.

To put that number in context, it’s about $2,000 more per student than the average tuition actually paid at Sidwell Friends, the prestigious school President Obama’s daughters attend. And it is more than fourfold the $5,928 average tuition charged last year by the private schools serving voucher students.

What’s more, the Opportunity Scholarship program does not take a dime away from D.C. public schools. On the contrary, the program brings with it an additional $13 million annually for the public schools — as part of a “sweetener” deal required to gain local and Democratic support at the time of its passage in 2004. Democrats apparently believe that a city with a $1.29 billion education honey pot requires an extra $13 million sweetener.

Needless to say, all that money does little good. The voucher students perform at least as well as public school students academically, and voucher parents are significantly happier with their chosen private schools than public school parents are with theirs, according to the Education Department’s official report on the program released last year.

What, then, is the real reason congressional leadership wants to kick these kids out of the private schools they love, and back into public schools? How can they turn a deaf ear to the YouTube videos of voucher-receiving students beseeching them to preserve the program? There is only one plausible explanation: They see the program as a threat to the public school employee unions at the core of their party.

If allowed to continue, these Opportunity Scholarships will keep reminding voters that independent and parochial schools are more efficient and responsive to parents than public schooling. That might accelerate the spread of private school choice programs around the country. But while two-thirds of public school employees are union members, only about 7 percent of the private sector work force belongs to a union. Many in Congress have apparently done this math, and fear the effect of real private school choice on their political futures.

That analysis is dangerously shortsighted. The D.C. program is just one among dozens of private school choice programs operating around the country. These education tax credits and vouchers have been growing steadily, and there’s no reason to expect that will stop. Congress is thus standing in front of a massive dike that is springing leaks. They have jammed their fingers into the hole that has arisen in D.C. for now. But the others will continue to widen and proliferate.

Other than pressure from the teachers’ unions, supporting school choice might be easier for opposing legislators than they think. Voucher programs cannot be constitutionally enacted at the federal level outside the District of Columbia. So all congressional leadership needs to do is allow the D.C. program to continue and offer moral support to their party colleagues at the state level who have increasingly begun to support education tax credit programs. And they can rightly cite Democratic statesman Daniel Patrick Moynihan — who supported education tax credits as far back as the 1970s — as an early leader in the movement.

But if they continue with their current tactics, our union-inspired Congress will soon find itself on the wrong side of history as the demand for choice in education grows louder.