Supreme Court conservatives target Obama on marriage law

[TupperHappy]

5. I think it can be reasonably implied

Consider this hypothetical. For the sake of argument say that the Supreme Court votes to uphold Section 5 of the Voting Rights Act. Further assume that in either 2016 or 2020, Rand Paul is elected President (I know, I know, snowballs, hell, but bear with me). A new challenge to the entire Voting Right Act is filed, and makes it all the way to the Supreme Court. And then President Rand decides to instruct the Solicitor General to not defend the law.

Would he be right in doing so? And how would that scenario be any different than what is happening now? Acts of Congress are presumed to be in accordance with the Constitution, and the President does swear an oath to uphold that Constitution. It seems to me that a President that refuses to defend a law that was lawfully passed by Congress (and signed by a previous president) is violating their oath of office.