I'm a little confused how a view which essentially returned to its initial point of origin can be described as "evolving". Maybe the public version of that view has evolved, but given that even the public view was this back in 1996, I'm guessing the only thing that changed was the height and relative importance of offices involved. In any case, we're back to adjudicating culture war talking points.
I don't see that this one in particular really harms or hurts Obama election wise. It's likely that it was harming him to hold out a middling view at this point; given a) that most Democrats/liberals overwhelmingly support gay marriage b) most Republicans don't, c) there's been a rapid shift in the last 5 years among minorities toward support, and d) those minorities were probably voting "Democratic" anyway. So I don't think talking over the election really matters here. Mitt Romney isn't Rick Santorum and isn't likely to turn this change in a public stance into a fire-breathing sermon over morality that overshadows other more pressing issues (or issues perceived as more pressing). This will more likely be just something that they will show a clear contrast on, rather than campaign centerpiece perspectives requiring intense debate.
What is of note is that Obama basically took the following perspectives
1) Continued to oppose state laws banning equal recognition, like the one passed in North Carolina, particularly in the form of amendments to state constitutions.
2) Continued to state that it was okay for states to make these determinations themselves.
I'm not entirely sure how those views square with each other. If these are badly crafted laws which violate respect for equal rights and recognition for some citizens unnecessarily (eg, these are not felons who have assaulted people or property), then I don't see why it is appropriate to permit governments at any level to pursue discriminatory policies. Even if these are more precisely crafted laws which may enjoy majoritarian support, that does not make them sensible policy. Perhaps that needle is threaded by making the argument that these are sloppy laws, but even the clear cut ones are openly discriminatory.
In fact, I find it a little strange that of all the various issues Obama has nodded some assent toward federalism, this is the one that he picks to actually evince real support for. And it's probably among the weakest for a federalist mentality. Even abortion to me has a stronger case for separate laws. This is far closer to slavery or other forms of discrimination which presently enjoy federal guarantees of protection. While there may be a highly pragmatic basis for this being a steady march toward equality undertaken at the state and local level rather than from federal interventions and court rulings, those court rulings are going to increasingly overturn bans anyway, and this will be a case where there are large intersections of conflicting state laws as people naturally begin to move between jurisdictions in a way that an issue like abortion can more easily resolve. One can simply travel to receive an abortion, an expense or a hassle, but not a denial of rights. One cannot travel to continue to have a legal marriage recognized in residence with its attending rights and benefits. Meanwhile, he seems perfectly comfortable thrashing state laws on narcotics or drug prescriptions, or on immigration, to take various points of perspective here.
I've also taken several thoughts out of debates with people who, at some level, continue to support bans or at least definitions of "traditional marriage".
1) It is not clear to most that the state has already crafted definitions which jar with "traditional" definitions of marriage, and thus created a civil institution distinct from this. Changing the definitions involved in civil and secular institutions does not automatically infer that religious doctrines and practices and rituals should have to change. Eg, that a definition of "traditional marriage" is not at all impacted by changing the state's definition of civil marriage laws. Mostly because the state's definition is not at all close to the premise of a traditional marriage (a corollary here would be that most people's definition of a "traditional marriage", at least in this country, is probably not what a "traditional marriage" would be according to their selected religious or theological doctrine). It's not clear to me how heterosexual couples would feel their pair bonding to be diminished if they no longer enjoyed a particular advantage in the form of state recognition over homosexual pair bonds, so long as their own advantages are not taken away from people who are unattached or are attached in less official capacities. Using examples such as the European experience with legal gay rights recognitions is a highly fraught enterprise that doesn't provide clear causation and in most cases, demonstrates that none of the feared difficulties will materialize as a result. (Example: Europe has long had trends toward lower birthrates and lower rates of marriage, which are among the apparent fears. These were not worsened significantly by adopting gay marriage laws. There are also a lot of cultural or economic causes that could be attributed here in some measure. Such as much higher rates of contraception use and at lower ages, higher ages at marriage, increased use of social welfare programmes, greater tolerance toward premarital or extramarital sexuality, etc).
2) It is not clear to most that the formation of "lesser" institutions, such as civil unions, indicates two further problems a) that they are not automatically endowed with the strongest equal recognition of rights and privileges accorded to civil marriages. Few people are aware of these distinctions in legal protections and advantages afforded to marriage but not to civil unions, even in states with very strong civil unions recognitions like Vermont b) More importantly. That because they are distinct institutions, they are more likely, as in the case of North Carolina, to be subjected to legal pressures and attacks, and perhaps even eliminated as distinct institutions altogether. Creating "separate but equal" institutions does not have a good track record in US history of actually performing the task of formal equality and seems a useless half-measure as a result.
3) It is not clear to most that the provision of state interventions in the form of benefits or privileges accorded to civil marriage recognitions and laws are not going anywhere. There are in fact some grounds on economic reasoning that the state should intervene in some fashions to protect or encourage this institution, though it is far from clear that the hundreds of laws that marriage law impacts are all necessary in and of themselves or that marriages should receive privileged status within them over other private contractual arrangements. In general, what I think to be the case is that people enjoy receiving special recognitions and protections for their private relationship choices, and that some of this recognition or protection may serve some social purposes (externalities) that justifies their continuing to do so. Therefore, marriage as a civil institution isn't going anywhere. I think a strong case can be made to amend some of those protections as useless or unnecessary, or to abolish or reform the laws that require said protections in the first place, but that's a separate issue from disentangling the entire thorny bed of laws surrounding the institution that on each point will receive strong advocacy and defence from the general public at large in order to say "we're not going to use the state to recognize marriages anymore, it will be all private contracts". Private contracts do not deal with things like our tax laws or immigration status or could be used to provide 5th amendment protections to spousal arrangements, etc. Yes you can use a will or insurance in a way you see fit, but you're already able to do this (for example nobody requires that you will an estate or decree an insurance policy to go to a spouse, it just presents some tax advantages to do so at present. Probably because most people probably would do so).
4) It is clear to most that apparently the title of the state's recognition matters in addition to any actual rights and privileges that are extended. I'm not sure how this helps the argument that a ban should exist, but they're at least aware of this much. What appears to be important to this point is that if the state were to create a distinct secular institution or abolish/reform its present legal frameworks that recognize that institution as "marriage", but instill in it all the present rights and privileges, most people feel that this institution would be diminished. I'm not persuaded that this is the case, as it would be a cosmetic change at best. But since the general public appears to be, I am persuaded that what you call it matters. Since this is the case, we are better off not bothering with distinct institutions that have different names. Both because the actual institution at question already has the aforementioned rights and benefits and I favor avoiding legal complexity as a general rule, and because distinct institutions for unfavored minorities have a poor track record of fulfilling equal status. Further, I'm not sure what the basis is to not recognize equal status of private relationships of this kind. Consenting adults of sound mind should be able to decide for themselves who they will love and cherish in lasting commitments to each other without interference from the state or from the general public deciding that these choices are inappropriate. Their friends and family may be entitled to such input over the course of a relationship, but why the state should receive that privilege seems an error in according powers to the state that it does not require.