The Bush-approved, US Constitutional amendment proposition reads as such:

Marriage in the United States shall consist only of the union of a man and a woman. Neither this constitution or the constitution of any state, nor state or federal law, shall be construed to require that marital status or the legal incidents thereof be conferred upon unmarried couples or groups.

As such, and as Professor Balkin explains, this seems to preclude marriage and civil unions for gays. That's quite a jump from the faily bipartisan support for allowing civil unions.