If John McCain is serious about school choice being a civil rights issue, perhaps he'd do well to revisit his party's longstanding efforts to ensure that public school districts remain segregated.
It was under the Nixon administration that the federal government fought busing programs and programs that made it possible for poor, minority, inner-city school kids to go to richer, whiter, suburban schools. The Nixon administration could have used its power to withhold Community Development Block Grant funds from municipalities, counties, and states that would not embrace affirmative measures. Instead they fought these measures and Republicans have made their resistance to regional, racial equality a hallmark of their policies ever since.
The Nixon administration even assisted with the fight against school integration in the (unfortunately) landmark case of Milliken v Bradley -- a direct attack on Brown v Board of Education.
Of course, this mentality has continued to today's Supreme Court in the recent school integration cases that included Justices Roberts and Alito -- the type of judges McCain says he wants on SCOTUS -- arguing against voluntary integration.
Here in the Chicago area, State Senator James Meeks used just this idea in his protest against unequal educational opportunities in the region.
The solution isn't to require poor people pay for private education while richer people get public education. It's to equalize the quality of education for everyone by removing the arbitrary barriers of school districts that perpetuate racial, ethnic, and income inequality.