Why don't all states require proof of citizenship?

Nebraska and Michigan were singled out in a story by The Associated Press as the only two states that require proof of citizenship to provide welfare benefits.

And it's true that the requirement is keeping people off the Medicaid rolls, according to a federal study done after the requirements were put in place at the national level.

"People are not getting the help they need and they're eligible for," said Sharon Parks of the Michigan League for Human Services in Lansing.

Unlike Michigan, where the applicant must pay for the birth certificate, Nebraska will foot the bill, resulting in little dropoff in welfare rolls here.

You can't blame Michigan for doing what it can to keep ineligible people out of the welfare system; it's one of the few states that give health care coverage automatically to children and adults on welfare. With the struggling auto industry, times are hard in Michigan, and a food assistance program, which is easier to qualify for, had a record number of participants last month.

Missouri plans to join Michigan and Nebraska in requiring proof of citizenship, and other states, like Virginia, at least require applicants to show a birth certificate, Social Security number, or at least sign an affidavit of citizenship.

For us, the obvious question is not why some states require strict proof of citizenship before providing benefits, it's why don't all of them?