WASHINGTON – Sharp questioning by the Supreme Court's conservative justices cast serious doubt Tuesday on the survival of the individual insurance requirement at the heart of President Barack Obama's historic health care overhaul.

Arguments at the high court focused on whether the mandate for virtually every American to have insurance "is a step beyond what our cases allow," in the words of Justice Anthony Kennedy.

But Kennedy, who is often the swing vote on cases that divide the justices along ideological lines, also said he recognized the magnitude of the nation's health care problem and seemed to suggest that it would require a comprehensive solution.