Jeffrey Rosen has an interesting piece on how the Supreme Court would treat the Obama administration circumventing a default by invoking the 14th Amendment. Since the House hasn't passed the relevant legislation yet, the question is worth considering. Rosen argues that the Court would be very unlikely to rule such an action unconstitutional for two reasons: 1) it would contradict existing precedent on standing and "political questions," and 2) a majority of the Court wouldn't want to do it anyway. I disagree with the first point but agree with the second.
The first argument is that the Supreme Court would decline to hear the case because there was no one who has standing to bring it. But I don't believe that, if they wanted to, a majority of the Supreme Court would not have any problem justifying a way around that. The conservatives on the Supreme Court have indeed narrowed standing rule in several cases...in which they were also substantively hostile to the legal claims being advanced. They've never narrowed standing to limit access to litigants they like, and I see no reason why they'd start here. More generally, as Rosen concedes, Bush v. Gore proves that the Court's conservatives will do anything they strongly want to do. And since the argument that the 14th Amendment does not give the president the authority to unilaterally prevent default is perfectly reasonable, a Bush v. Gore-type legal atrocity would hardly be necessary in any case. The Constitution plausibly allows justices to side with either party here.
So the real question is whether the Supreme Court would want to rule such an action unconstitutional, and here I think Rosen is correct in deciding that Obama would win. The Supreme Court has little to gain, and much to lose, if it essentially orders the federal government to default on the national debt. It's likely that a majority would do it, therefore, only if it advanced very cherished goals. I don't see that it does. Ruling against our hypothetical Obama does not, as far as I can tell, do anything to advance conservative legal goals, and as Rosen says in the case of Scalia and Thomas (who generally favor strong executive power) would actually be in tension with them. In terms of non-legal goals, where in Bush v. Gore the stakes were clear, here they're muddy and speculative. A Supreme Court decision ordering the government to default might advance conservative policy goals, but it might not, and especially a 5-4 decision along ideological lines would if anything give Obama more political authority in subsequent negotiations.
The bottom line is that while there might be good reasons for Obama not to pursue such a course if it comes to that, I agree with Rosen that fear of the Supreme Court should not be one of them. Obama can probably do this if he wants to.