WASHINGTON – The Supreme Court’s 5-4 decision upholding the nation’s health care law marks an enormous political victory for President Obama in the heat of a re-election campaign, and affirmation as well for the Democrats’ decades-long campaign to extend coverage to millions of Americans who now go without.

But if the sweeping changes mandated by the law will go forward, so, too, will the political controversy.

Presidential challenger Mitt Romney and Republicans seeking control of Congress will see to that, seizing already on Chief Justice John Roberts’ ruling that the law levies a new tax on anyone refusing to purchase coverage.

The decision was rich in irony as well as history.

It was the second time in four days – a ruling Monday threw out much of an Arizona state law on immigration – that a Roberts’-led majority upheld the Obama administration’s position on a noisy, contentious issue that has roiled the country’s politics for years.

The chief justice came into office in 2005 as the brightest star of a younger generation of conservative legal experts, a man whose resume suggested he had been virtually groomed for the high court.

Adept politically, he disarmed his critics when he told his confirmation hearing that a judge’s role was “to call balls and strikes, and not to pitch and bat.”

One who was not persuaded at the time was then-Sen. Barack Obama, campaigning for the support of liberals and other Democratic primary voters as he pursued the party’s presidential nomination.

He pronounced Roberts qualified for the high court, but then added that throughout the nominee’s legal career to date, “he has far more often used his formidable skills on behalf of the strong in opposition to the weak.”

On this case, at least, Roberts seemed to be ruling through gritted teeth.

“We do not consider whether the (law) embodies sound policies,” he wrote of the health-care legislation that Republicans have vowed to erase. “That judgment is entrusted to the Nation’s elected leaders.”

That was a reference to Obama and the lawmakers of both parties in Congress, whose disagreement is so deep that nary a Republican voted for the legislation when it slogged to passage in 2010.

The polling then – as now – makes the law out to be a political negative, and Obama acknowledged as much in understated remarks at the White House.

“It should be pretty clear by now that I didn’t do this because it was good politics,” he said. “I did it because I believed it was good for the country. I did it because I believed it was good for the American people.”

For the first time since Obama signed the bill into law, the president and advocates of the measure have the law and the Supreme Court on their side, and a clearer path toward implementing the legislation.