I haven't seen any discussion of what seems to me a likely motive for the Democrats' persistence in pushing the genocide resolution.
The Democrats have been unable to muster the political will-muscle combination to force a withdrawal from Iraq. However, passing this resolution is likely to do serious, possibly fatal, harm to the Iraq military mission. Turkey may well withdraw various key permissions. Our position might finally become as untenable as the Democrats keep pretending it already is. Gee, I wonder who'd be happy about that (aside from AQ in Iraq, Iran, etc.)?
This way, they can undercut "Bush's war" while acting self-righteous about something supposedly unrelated.
UPDATE: At least one commentator has now made this point -- Thomas Sowell.