Via Rick Hasen, the district court in Kansas has ruled for Secretary of State Kris Kobach in his crusade to demand citizenship in exchange for voter ID. Here's the key, I think:

Arizona and Kansas have established that their state laws require their election officials to assess the eligibility of voters by examining proof of their U.S. citizenship beyond a   mere oath. The EAC decision makes the case that the states have other means available to   enforce the citizenship requirement. But the Arizona and Kansas legislatures have decided that   a mere oath is not sufficient to effectuate their citizenship requirements and that concrete proof   of citizenship is required to register to vote. Because the Constitution gives the states exclusive   authority to set voter qualifications under the Qualifications Clause, and because no clear   congressional enactment attempts to preempt this authority, the Court finds that the states’   determination that a mere oath is not sufficient is all the states are required to establish.  

Hasen explains why it matters, in detail, but the short version is this: Republicans have warred for years against the "motor-voter" law, the Clinton-era reform that allows you to get your voter registration at the DMV. One of the goals of the new citizenship requirement was preventing easy registration in Kansas. In the short term, Kobach has succeeded.