Why can't you find a record of him publicly saying so? If it's just an established check and balance in our system, why can't you produce evidence of him saying "I'm not enforcing this law because I disagree with it" in any forum in which he could be held accountable (or not accountable, per your theory) for that decision?
Here's why: because it's not!
Here's SCOTUS in Kendall v United States:
> To contend that the obligations imposed on the President to see the laws faithfully executed implies a power to forbid their execution is a novel construction of the Constitution, and is entirely inadmissible.
> "This doctrine cannot receive the sanction of this Court. It would be vesting in the President a dispensing power which has no countenance for its support in any part of the Constitution, and is asserting a principle which, if carried out in its results to all cases falling within it, would be clothing the President with a power to control the legislation of Congress and paralyze the administration of justice."
> The result of the cases of McIntire v. Wood and McCluny v. Silliman clearly is that the [court's authority to command an officer of the United States] to perform a specific act required by a law of the United States is within the scope of the judicial powers of the United States under the Constitution"