The most likely, and politically feasible, scenario is that Romney will not try to act unilaterally and instead will use his presidential bully pulpit to encourage Congress to repeal the bill.
"He's not a hapless giant by any means," said Stephen Hess, a senior fellow emeritus at the Brookings Institution. "He's more powerful than any other single individual around, but it's a system that doesn't allow him to just go ahead and do away with a major act of Congress."
With 47 Republicans in the Senate and 60 votes required to repeal in the upper chamber, even a great night on Nov. 6, 2012, is unlikely to produce a filibuster-proof GOP Senate majority. When the Senate voted in early 2011 on repeal, the vote failed 47-51. Obviously, it will take convincing some Senate Democrats to cross party lines to repeal the bill in Congress.
If Republicans won a simple majority of 51 seats in the Senate, a more possible scenario, they could attempt to repeal the law using reconciliation, a procedural maneuver that would require a simple majority instead of 60 votes. But this politically toxic long-shot would take time to concoct and would not meet Romney's "first day" timeframe.
Now, repeal has re-emerged as a top campaign issue for congressional Republicans, much like the 2010 midterm elections that swept Rep John. Boehner into the speaker's chair.
"It becomes a huge issue going forward to the election in November," Rep. Steve King, R-Iowa, told ABC on the steps of the court immediately after the decision was announced. "Barack Obama has had this around his neck for two and a half years. It will become an albatross around the neck of Barack Obama walking into November."
Asked why it is necessary for the House to act again on repeal, particularly when there are not enough votes in the Senate to repeal it, Boehner also said the Supreme Court's ruling will only act to strengthen his party's resolve this fall.
"The real outcome of today's decision is to strengthen our resolve to make sure that this law is in fact repealed," Boehner, R-Ohio, said. "We're going to work every single day between now and Election Day, and the American people then will get an opportunity to make their decision on Election Day because elections have consequences. The election in 2008 clearly had a consequence that most Americans disagree with."
After Chief Justice Roberts made it clear that the individual mandate was within Congress's power to tax, Rep. Pete Sessions, the chairman of the National Republican Congressional Campaign committee, said Republicans "will call it what it is" as they work to magnify the Democrats efforts to increase taxes.
"It is a tax," Sessions, R-Texas, told reporters in the Speaker's Lobby during votes this morning. "Obama will be a one-term president as a result of this bill."