Although the law survived the court challenge, it faces an uncertain future. Republican presidential candidate Mitt Romney and GOP congressional leaders have pledged to repeal the law if they take control of Congress and the White House in November elections.

The court's decision, while a relief to Democrats, could further energize voters who dislike the law to back Republicans in November. And it forces the Obama administration to continue defending the unpopular insurance mandate.

On the other hand, the court's blessing could itself shape public opinion of the law, particularly among independents and undecided voters who view the justices as relatively free of the partisan agendas of the government's elected branches. Polls consistently show that the public places greater confidence in the Supreme Court than either Congress or the presidency, although the justices' approval ratings have slipped somewhat over the past year.

Eoin Treacy's view In a bid to cushion the potential threat posed to margins by healthcare reform insurance companies have been aggressively raising premiums. The result has been that a considerable number of related share prices have outperformed the wider market. The Supreme Court's decision crystalises the risk to margins and has contributed to some quite extreme volatility today.

UnitedHealth Group (1.45%) has been a relative outperformer but has paused in the region of the 2008 peak over the last few months. The share has found support in the region of the 200-day MA on successive occasions since 2010 and a sustained move below it would be required to question medium-term uptrend consistency.

Aetna (1.77%), Cigna (0.09%), Humana (1.26%) all dropped abruptly in May and encountered resistance in the region of the 200-day MA this week. A sustained move back above the MA is the minimum requirement to question potential for additional weakness.

Life/Health insurers Torchmark Corp and Primerica are both worthy of mention. They both found support in the region of their respective 200-day MAs this week and a sustained move below their trend means would be required to check the consistency of their medium-term uptrends.