But even if the White House is a fortress of message discipline, it cannot disguise the potential heartbreak for Mr. Obama, who managed to achieve a decades-old Democratic dream despite long odds and at steep cost.

If he loses both his law and re-election, many will conclude “that he bet on his major reform, and the Supreme Court defeated it, and he lost his hold on the presidency,” Robert Dallek, the presidential historian, said in an interview…

But there are clues that Mr. Obama is privately grappling with both the potential loss of universal health care and how much of it he might be able to restore. At a recent fund-raiser in Manhattan, he rattled off a second-term agenda, and along with tax reform and immigration, he mentioned coming back to health care, to work around a negative ruling. His tone was matter-of-fact, one attendee said.

If the court strikes down the mandate and Mr. Obama wins in November, he could face one last version of his perpetual choice on health care: would he settle, learning to live with a sharply edited law? (Given that Republicans see the bill as a signature piece of big-government overreach, he might have no choice.) Or would he expend yet more precious capital on health care?