That has got to be the absolute worst excuse for signing an UnConsitiutional piece of legislation I have ever heard.
Let's use your implied definition of what the "oath of office" entails and apply it to a few things and see if President Jhoffa is violating his oath of office if he does not issue and EO overturning or refusing to enforce the following "unconstitutional" laws on the books
Roe v. Wade
The Brady Bill
Nafta
The war on drugs
The CFR that the new one replaces
Flag burning as political speech
If the president violates his oath by passing laws he has constitutional reservations with, is he not violating his oath when he enforces laws that large segments and even he feels are equally unconstitutional?