Yesterday they issued another decision that I think they decided correctly. They struck down an Arizona law requiring people to submit proof of citizenship before using a federal form to apply for a voter registration certificate (as required under the 1993 National Voter Registration Act -- the so-called "Motor Voter" law). They ruled it was unconstitutional for the state to add requirements for complying with a federal law.
I'm sure we'll be hearing right-wingers whine that this will allow non-citizens to vote in our elections. That is nonsense. This decision doesn't change the requirements to get a voter registration in any way -- it simply upholds the easy application for a voter registration certificate, which is exactly what was intended by the federal law (to make applying easier for citizens).
What the decision does is to state unequivocally that a state cannot change a federal law -- by either adding or removing requirements for complying with that federal law. The only entity that can change the requirements of a federal law is the federal government itself.
This may not sound like too important a decision to some, but it is very important -- especially in this era of state Republican governments trying to alter or even eliminate certain federal laws in their particular state. And the decision could be applicable in areas other than voting rights (such as federal gun laws or health care laws).
The Supreme Court got this one right.