Responding to Thursday’s Supreme Court decision upholding the constitutionality of the Affordable Care Act, Congressional Republicans have scheduled a vote in the House to repeal the law and Mitt Romney pledged to undo the measure if he’s elected president in November. But unless the GOP wins a super majority in the Senate — a scenario no one thinks is plausible — it can do little more than weaken Obamacare’s regulations and defund some of its provisions. Here is why: