Incoming brief by federal legislators
DC had an Congressional amicus brief supporting it, signed by, I forget, 16 or 17 House members.
According to this article, there is a Heller brief incoming, supporting the individual right position, signed by 250 House members and 57 Senators. A majority of both Houses. And from that, necessarily bipartisan.
Hat tip to reader Jack Anderson.
UPDATE: the Washington Examiner reports that 68 House Demos, and 9 Demo Senators, are on the brief. Which means that the brief supporting Heller has four times as many Democratic signers as did the one supporting the District's gun law.