I have just written this commentary for Slate. It concludes:

If the current D.C. voting rights law is indeed unconstitutional, then the only way to get D.C. a full House member is the way that gave district residents the right to vote for president: a constitutional amendment that would either make D.C. a state, give it a member of Congress (and possibly two senators) without making it a state, or merge D.C. back into a neighboring state, such as Maryland. But constitutional amendments are extremely difficult to pass, requiring a vote of two-thirds of Congress and three-fourths of the states. With a country preoccupied by the most serious economic troubles of our lifetimes and two wars, voting rights for D.C. is not at the top of the list. Despite broad public support for some form of voting rights for D.C., the forces of inertia are strong.
This is precisely why Congress should pass the current law, even if it is likely to be struck down by the Supreme Court. Rejection by the court would put the issue on the front burner. Obama could then push for quick passage of a constitutional amendment in Congress and the states. He could remind people that many of our most important advances to voting rights have come through constitutional amendment, including enfranchisement of African-Americans, women, 18-year-olds, D.C. residents (in presidential elections), and those too poor to pay a poll tax to vote in federal elections.
The lack of voting rights for residents of Washington, D.C., is an example of what law professors call “constitutional stupidities.” Given this country’s commitment to equal voting rights for all, there’s no legitimate policy reason to deny congressional representation to the District’s residents. If that’s right, then the only argument I can see against a vote for the D.C. bill is that it could be viewed as violating the oath taken by members of Congress and the president to uphold the Constitution. But with legitimate arguments by credible legal scholars in favor of the bill, the constitutional question is not settled. Members of Congress can vote for D.C. voting rights in good conscience. Then we’ll see what happens next.

UPDATE: Brian Kalt responds.