The Department of Homeland Security announced a proposal to sharply tighten immigration rules today. Some immigrants who use welfare programs that they are legally entitled to use, like food assistance and housing vouchers, could be denied green cards because they use those programs. It's already been a rule that, in order to get a green card, an applicant can't be what is known as a public charge.It's a phrase that goes all the way back into the 19th century in our immigration laws. Basically, it means an immigrant who relies primarily on the federal government. It has been interpreted traditionally to mean cash benefits, like welfare. But this is the first time that an administration has really proposed extending the notion of a public charge to noncash benefits - the housing, the health insurance, the nutrition assistance. And it's something that the administrations have not done before, perhaps because Congress has decided that immigrants should be entitled to use these programs. We're talking, of course, about legal immigrants.