Click on the title above to link to a fascinating debate on Presidential signing statements.
This is one of the most interesting debates on Constitutional law that I have seen for many years, all the more so because it pits a conservative spouting Originalist arguments against a conservative spouting something else. The Originalist happens to be arguing against our Republican president's ability to attach signing statements to bills that he is signing, while at the same time believing that one or more aspects of the bill are unconstitutional.
First, the answer: Fein wins. As much as I like Ed Whelan, I find Fein's arguments compelling, inasmuch as he would have our government and Constitution work as it ought to, not necessarily as it does.
Whelan's argument that there is plenty of precedent for President's signing bills which include provisions deemed unconstitutional is not satisfactory. Just because somebody did something incorrectly before is not a reason to continue doing it incorrectly today.
It is perfectly reasonable to veto an entire bill because one or more provisions are deemed unconstitutional. Send it back to Congress where they can correct those particular provisions. That kind of horse-trading happens all the time. Government will not shut down. If it is effectively similar to a line-item veto, then so be it.
There is a difference, however, between this type of veto, and a line item veto; a line item veto could be used for whatever purpose, including politcal ones. That is very different indeed from a President determining that a provision of a bill is unconstitutional, and sending the whole bill back to Congress with a note saying so.
There is much to be discussed here, and I've only begun to scratch the surface. I will try to get back to it shortly.