Although Pence needs to try to win votes for Trump with whatever Pence says about these issues, since the states have never delegated to the feds, expressly via the Constitution, the specific powers to regulate either abortion or marriage, discussion of such issues by candidates for federal office is ultimately a waste of time imo.
”From the accepted doctrine that the United States is a government of delegated powers, it follows that those not expressly granted, or reasonably to be implied from such as are conferred, are reserved to the states, or to the people. To forestall any suggestion to the contrary, the Tenth Amendment was adopted. The same proposition, otherwise stated, is that powers not granted are prohibited [emphasis added].” —United States v. Butler, 1936.
You are entirely correct.