The Affordable Care Act is safe from the courts. But Mitt Romney has vowed to repeal the law on day one of his presidency. Would he really do that?

That depends on two things: how far a slim Republican majority in the Senate would be willing to push — and how insistent Republican activists and aligned interest groups would be that they push as hard as possible.

Ryan Lizza argues that repeal wouldn’t be feasible under Senate rules, at least not against 41 or more senators who are willing to fight hard against repeal. For more on reconciliation and just how exactly the various rules apply, I recommend Sarah Binder’s notes on the legislative effects of the Court’s ruling.

But I’d emphasize one bottom-line fact: An intense majority in the Senate really can, ultimately, do whatever it wants, as long as it’s willing to sacrifice logic, reason and respectability on the way to getting there.

Is it a problem under Senate rules to use reconciliation for something that increases the deficit? Change the rules — or change the Congressional Budget Office until it reports the “correct” score. Can a filibuster stop some things? Not if the Senate majority invents a new “Broccoli Tyranny” exception to filibuster rules, just as many Republicans during the George W. Bush presidency invented, and almost passed, a judicial nominees exception.

Yes, there are real constraints against just rewriting the rules whenever they want. That’s why Democrats didn’t do it in 2009 and 2010. But still repeal could be done.

So the real question is: How strong will the incentive for Republicans to go through with repeal be? David Frum argues today that the incentive might not be so strong after all. Don’t forget, he reminds us, that if the Medicare doughnut hole is reopened that you’ll have seniors angry at Romney and Republicans in Congress — just as young people will be angry if they’re kicked off their parents insurance.

We don’t know how all of this will play out. But I wouldn’t underestimate how symbolically important repeal has come to be for Republican primary voters — or the extent to which Republican members of Congress fear those voters and the organized groups who keep them paranoid about being seen as RINOs.

And there are plenty of other ways Republicans could undermine the law, to the extent that repeal would become irrelevant.

It comes down to this: Would President Romney and a Republican Congress care more about alienating constituencies benefiting from the law or more about the symbolic importance to their base of eliminating Obamacare once and for all? Because they could eliminate Obamacare if they wanted to — no matter what the “rules” say.