Is the Constitution in the way of DC statehood?

In an op-ed for The Hill, ACS President Russ Feingold counters recent claims about the topic of D.C. statehood being contingent on a constitutional amendment. In addition to highlighting the politicized nature of this argument against pursuing D.C. statehood, Feingold states:

"We should not allow politically driven calls for a constitutional amendment, which most observers know is not in the offing, as reason to perpetuate the racist denial of D.C. statehood. Our democratic legitimacy is permanently undermined so long as D.C. residents are denied full representation."