Until recently, Justice Clarence Thomas, the Supreme Court’s only black member, has been little noticed and often dismissed as an intellectual lightweight, a token appointee of President George H.W. Bush. In a rather abrupt change, both his stature and his ethics have come under scrutiny.

As to his stature, while usually siding quietly with the conservative bloc, he now is seen as an influential leader of that group, bringing them along to extreme conservatism. Jeffrey Toobin, the New Yorker magazine’s legal analyst, made that point in as recent issue.

He cites areas where the court has moved to the right: free speech rights of corporations, the rights of gun owners, and potentially, the powers of the federal government.

“In each of these areas, the majority has followed where Thomas has been leading for a decade or more. Rarely has a Supreme Court justice enjoyed such broad or significant vindication.”

When the court court overthrew the Brady gun control law in 1993, Justice Antonin Scalia’s majority opinion concluded that the measure was an impermissible intrusion on states’ rights. Mr. Thomas’s concurring opinion broke new ground, suggesting that the Brady law might have been unconstitutional as violation of the Second Amendment. He foresaw a future possible decision interpreting the amendment guaranteeing a personal right to bear arms instead of merely referring to state militias. That opinion led to a campaign by the National Rifle Association that ended with the court’s 2008 decision holding that the amendment gives individuals the right to bear arms.

Mr. Toobin’s article raises that question of ethics and involves the Justice’s wife, Virginia. The article is titled “Partners: Will Clarence and Virginia Thomas succeed in killing Obama’s health care plan?”

Virginia Thomas has been an active opponent of the new health care law. And Justice Thomas, under pressure from critics, publicly released details of her income from working for groups fighting the health care reform law.

She had started a nonprofit organization called Liberty Central and as its president and CEO received $150,000 in salary as well as money from a health care lobbying firm she created. Mr. Thomas made the belated disclosure with the explanation that he had misunderstood the requirements.

Seventy-four House Democrats later signed a letter to Justice Thomas asking that he recuse himself if the health care law comes before the court. They said that Virginia Thomas’s work as a lobbyist “creates the appearance of a conflict of interest.”

Mr. Thomas cracked back at his critics in a speech at a conference of the conservative Federalist Society. He said they “seem to be bent on undermining” the legitimacy of the Supreme Court as an institution. He went on: “There’s going to be a day when you need these institutions to be credible and to be fully functioning to protect your liberties.”

A court challenge seems sure to come. And Justice Thomas certainly will not recuse himself, since Supreme Court justices are exempt from the federal judicial code of ethics.

The justice, who as a nominee 20 years ago spawned a national debate over sexual harassment in the workplace, could decide the outcome of the decade’s most sweeping legislation.