When Chief Justice John G. Roberts Jr. joined with the court’s liberal justices to uphold President Obama’s health-care law, it was historic in more ways than one: It was only the second time in his seven years on the court that he provided the winning vote for the left to prevail over the conservative justices.
That statistic alone should be enough to cool hopeful chatter from some liberal political commentators that perhaps Roberts is showing signs of becoming the next David H. Souter. Souter, nominated to the court in 1990 by President George H.W. Bush, eventually became a fairly reliable liberal vote.

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An analysis of the 2011-2012 Supreme Court session, including justice voting patterns and key cases.

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But it does point to another fact about the Supreme Court term that ended last week: In cases that divided the court into its usual ideological camps, liberals were in the majority as often as conservatives.
Justice Anthony M. Kennedy, who normally provides the decision vote when liberals and conservatives disagree, sides about two-thirds of the time with conservatives. This term, according to statistics at SCOTUSblog, he split the difference evenly.
And on the two issues most likely to define the court’s term — health care and Arizona’s get-tough law on illegal immigration — liberal justices Ruth Bader Ginsburg, Stephen G. Breyer, Sonia Sotomayor and Elena Kagan were in the majority.
The limit of federal power was the overarching theme of the court’s deliberations this term, and it delivered a mixed verdict.
Kennedy and Roberts parted ways with conservatives Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr. in the Arizona case. Kennedy’s majority opinion was a solid affirmation that the federal government must play the preeminent role in immigration policy and that states must be careful in trying to supplement it.
“Arizona may have under­standable frustrations with the problems caused by illegal immigration,” Kennedy wrote. “But the state may not pursue policies that undermine federal law.”
The health-care ruling, like the immigration decision, was an important political win for the Obama administration. But it came with new restrictions on federal authority. Roberts and Kennedy joined the other conservatives in saying the requirement that almost all Americans must buy health insurance was not constitutional under Congress’s authority to regulate interstate commerce.
“The Commerce Clause is not a general license to regulate an individual from cradle to grave,” Roberts wrote, although he found the individual mandate constitutional under Congress’s taxing authority.
Ginsburg said the Commerce Clause finding was disturbing.
“Since 1937, the court has deferred, as it should, to Congress’ policymaking in the economic and social realm,” she said in a dissent read from the bench.
And seven members of the court, all but Ginsburg and Sotomayor, said there are limits to how coercive Congress may be when conditioning federal payments to the states on requirements the states must perform.
Stanford University law professor Pamela Karlan said Roberts’s health-care compromise was “certainly designed to make the court look less political. But in fact it is setting the seeds for the future.”