Obama health reform law: clues to how the justices might behave

Predicting US Supreme Court decisions is often compared to reading tea leaves, and is frequently much less accurate. But there are some clues about how the justices may approach their assessment of the constitutionality of the Patient Protection and Affordable Care Act (ACA).

Analysts expect the four members of the court's liberal wing – Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor, and Elena Kagan – to vote to uphold the constitutionality of the ACA's individual mandate.

Analysts are less certain about how members of the court's conservative wing might behave.

Some observers have cited Justice Antonin Scalia's concurrence in a 2005 case in California upholding the federal government's power to prosecute the use of medical marijuana even when the drug was home grown and home-consumed legally under a state law.

In upholding the applicability of federal drug laws, the court – and Justice Scalia – found that the regulation necessarily reached home use of medical marijuana because such activities might otherwise undermine the comprehensive federal scheme to ban marijuana.

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Five years later, in a case called US v. Comstock, the high court again embraced a broad reading of the scope of federal power when it upheld a law that authorized the continued detention of sexual offenders after they had served their criminal sentences.

The law was challenged on grounds that Congress exceeded its constitutional authority in passing the detention law. The justices upheld the law 7 to 2.

In that case, Scalia joined a dissent written by Justice Clarence Thomas denouncing the government's underlying justification for the federal detention law as a pretext to encroach into areas assigned solely to state governments.

The Comstock decision is important because three members of the court's conservative wing joined the majority opinion.

Two of those members, Justice Anthony Kennedy and Justice Samuel Alito, wrote concurrences distancing themselves from the majority opinion's expansive reading of federal authority.

Unlike Justices Kennedy and Alito, the third conservative in that majority opinion – Chief Justice John Roberts – offered no written explanation of his view of the case.

Some analysts speculate that Kennedy may be the most likely justice to swing to the liberal side of the court and provide a fifth vote to affirm the ACA.

From his prior decisions, the one justice who seems least likely to vote to uphold the ACA is Justice Thomas.

In the meantime, legal scholars and journalists will be listening closely during oral argument to the tone and character of questions posed by the justices to try to discern revealing hints of which way they may be leaning.