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It was a blockbuster decision by the Supreme Court today to uphold President Obama's signature piece of legislation - health care.

Five months before the presidential election the court delivered a win to the White House with a 5 to 4 decision and Chief Justice John Roberts writing the majority opinion.

Many in the White House advised Obama to focus on the economy instead of health care in his first term. But he went for it. And despite facing unanimous opposition from Republicans in Congress the bill was passed and now the Supreme Court has upheld it.

Had the court's decision gone the other way Mitt Romney would have made the case that Obama's first three years were "wasted" since the Supreme Court struck down the law. In fact, Romney began to make this argument last night at a rally in Northern Virginia.

Today's decision is what the White House was hoping for, but not necessarily what they expected. And it is certainly a win. But the question now is can Obama turn health care into a popular piece of legislation?

Our latest poll shows that most Americans don't favor this law even though they support many of its provisions, such as not being denied health care due to preexisting conditions.

But after today's decision does the validation from the Chief Justice, a conservative and President George W. Bush appointee, become something of a Good Housekeeping seal of approval? Will that, combined with Obama's ability to argue for this law, eventually make the Patient Protection and Affordable Care Act more popular as we approach November 6?

It's a very clean political fight. The president will continue to say 'I will push for the law that has been upheld by the court.'

Mitt Romney will lead the Republicans calling for repeal. And in some ways life is a little easier for House Republicans than Romney because they don't share as much of the burden of explaining how they will replace the most popular parts of the law.

My Bottom Line: It's a big win for the White House and President Obama. It's a mixed bag politically for Mitt Romney and Republicans going forward.

And the biggest question now is what will it mean for the legacy of Chief Justice Roberts? My bet is this will be seen as THE decision of his tenure.

- George Stephanopoulos