Your flaw is in thinking "a few malcontents on the internet" constitute The Public (itself a convenient fiction).
Obama's response is already pre-determined. It is "fuck you, you already voted for me. If it bothers you so much, cast a ballot for Gingrinch. Or Nader. Ahahahaha".
The Public is just one interest group, 50% of whom don't ever vote, and, of the remaining 50%, roughly 45% will vote for one particular party because of the beastly, partisan and naked ideological commitment of the other, 45% do the same for the opposing party, 2.5% are "independents" who vote based on an ill-concieved notion of political centrism and 2.5% support third parties.
The Public aint shit compared to Goldman Sachs, Wackenhut or the Pentagon. The only way this law is going to get repealed is if someone goes to far and locks up Somone Important and With Connections, ie; a member of the ruling elite. Until then, The Public will just have to suck it up.
I have an honest question regarding realpolitik: Is there a general line that could realistically be crossed that would make an online petition effective? Sure, a few thousand mouse clicks won't do much, but what about a million? 1.5 million? 1.57 million? (Which, at that point would be over half of the population...)
What I'm trying to say is whether there's some point where the "people", while not having the physical or monetary resources to compete with Government Inc., would somehow hit a psychological limit that would indeed influence Obama's behavior; and if that limit is realistically possible to reach.
Is there a tipping point for public opinion affecting policy? Sure.
But, you have to consider the particulars of the political situation. In 2007-8, the Democratic Congress enshrined, legalized and expanded the power of the Executive massively, despite a Republican President being in charge. Why? Because they knew they had a good chance at seizing the Presidency in 2008 and so those powers would become their
Same dynamic is at play here. Even if Obama threatened to veto the bill, what would happen? The Republicans would put the legislation somewhere cosy, wait until a Republican President was in the White House and then try it all over again. And almost certainly succeed.
There are other things can they do as well. They can sneak in the provisions under funding Bills, social security-related legislation, healthcare reform and so on. Things which Obama's base would punish him for if he refused. Which he wont, because he has accepted the Bush-Cheney view on counter-terrorism and civil liberties, but even if he hypothetically did not, the vast majority of the ruling class do.
And that's the thing. The ruling class interests are aligned in such a way that even elite dissenters are unable to effectively fight back against it. Feingold, Ron Paul, Alan Grayson (before he lost his election) and so on have the luxury of speaking out, because they're already effectively sidelined.
One of the other unique factors influencing US politics is the high degree of partisan affiliation among the grass roots voters, while there is a good deal of agreement at the higher levels, especially on issues concerning National Security, Finance and so on. Therefore, the chances of a unified front among the general population are low, as those who try to do so will invariably be labelled as party traitors by their own side, and marginalized as a consequence. Usually, bipartisan movements in the US are those which agree with the National Security/Financial policy situation, such as the alliance between humanitarian interventionists and neoconservative hawks over Iraq, or the agreement between Republicans and Democrats over bailing out the banks.
As such, any mildly competent administration can play these factions like puppets, setting one group against another (usually via the media gossips, who are for the most part the useful idiots of the ruling class, but still somewhat more savvy than the general public) and achieve the outcome that is desired. But that outcome is set by the bipartisan consensus of the ruling class, which is not only the executive/senate/house but also the "invisible government" of influential think tanks, investment banks, the military, spooks and so on. There are, of course, factional struggles and disagreements within this grouping. But, by and large, what they say goes. When they decide what it is they are saying.