Fifty-nine senators, representing (as explained here) some 63 percent of the American public, accompanied by a large House majority and a president recently elected with 70 million votes, cannot enact changes in the nation's health-care system that have been debated for decades.
A 59-41 margin is not enough for a change of this magnitude.

Five Justices of the Supreme Court, outvoting their four colleagues, can work a fundamental change in election law that goes far beyond the issues presented by the parties to the case. (Among many accounts, see these two on Slate, here and here, and National Journal here.) Courts always have the option of deciding cases narrowly or broadly. The breadth of this one, reaching far beyond the merits of the case so as to enact the majority Justices' views, is staggering even to a non-lawyer like me. A one-person margin* is enough for a change of this magnitude.

In the least accountable branch of government, the narrowest margin prevails; in our elected legislative branch, substantial majorities are neutered. My current article strikes a somewhat optimistic tone, in concluding that the only truly broken part of our country is its system of government. (Everyone on Earth would like to imitate America's universities. No one is copying our current governmental machinery.) But that brokenness will require some creativity to repair, and soon.
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* Yes, by definition a nine-member Supreme Court will end up making some 5-4 decisions. But it is impressive how many Big cases, from Marbury v Madison (5-0) to Brown v Board of Education (9-0) to NY Times v Sullivan (9-0) to  United States v Nixon (8-0), have not been cliffhangers -- and how disturbing and friction-engendering a one-vote decision can be when, as in this case, it seems to turn not on any change in real-world circumstances but simply on who now sits on the court. For another time: how John Roberts' "Hey, I'm just here as a neutral umpire, to call balls and strikes" confirmation testimony in 2005 would seem if viewed again today.