John Murray, a spokesman for Representative Eric Cantor of Virginia, the second-ranking Republican in the House, said that if control of the House flips, possible targets for defunding may be the insurance exchanges, the new agency set up under the law to compare different drugs’ effectiveness and any added staffing that may be sought to manage coverage expansions.

By vetoing spending measures that don’t include money for the law, Obama may set up a situation similar to the 1995 government shutdown triggered by a spending dispute between the then Republican-controlled Congress and Democratic President Bill Clinton.

That shutdown hurt the Republicans, who lost congressional seats in 1996. James T. Walsh, a former Republican chairman of Tiahrt’s panel, said Republicans could dodge blame this time by portraying Obama as the instigator.

“If the president precipitates that, then the president precipitated it,” said Walsh, who is now a lobbyist for the Washington firm K&L Gates. Republicans should just “go about their business,” he said.