Advocates for stricter voter ID laws are pushing new measures in some states to require driver's license or partial Social Security numbers on mail-in ballots. In California, Colorado and Nevada, these proposals are on the midterm election ballots. The voter identification measures are among about 30 ballot questions affecting state voting policies. They reflect an ongoing debate about election participation and security. Six states are considering measures reaffirming that only citizens can vote. Several states are considering measures that could make it harder to pass constitutional amendments or tax hikes. By contrast, a Missouri measure would make it harder for lawmakers to change voter-approved citizen initiatives.