See Page 297 of Davidson and the 3/7 Blog Post

At The Washington Post, Aaron Blake reports that the Secretary of the Treasury does not know much about the item veto.

[I]n discussing the topic with Chris Wallace, Mnuchin appeared unfamiliar with even the basics of the line-item veto, which was struck down by the Supreme Court in the 1990s.
Here's the exchange:

MNUCHIN: As you heard him say, he's not planning on [signing an omnibus] again. I think they should give the president a line-item veto. These things should be looked at —
WALLACE: But that's been ruled unconstitutional by the Supreme Court, sir.
MNUCHIN: Well, again, Congress could pass a rule, okay, that allows them to do it. But —
WALLACE: No, no, sir, it would be a constitutional amendment.
MNUCHIN: Chris, we don't — we don't need to get into a debate in terms of — there's different ways of doing this. My comment is, it's clear what happened.

Two things.

First, Mnuchin's comment that Congress could simply pass a rule is wrong. Even if you consider proposing a constitutional amendment to be “passing a rule,” it would require two-thirds majorities of both chambers and ratification by 38 out of 50 states. In other words, Congress can't do this on its own.

The second thing is that Mnuchin seems to suggest there is a “debate” to be had about the “different ways of doing this.” But there isn't — not really.

“Mnuchin probably doesn’t know that there was a real-life experiment in the 1990s that answered this question,” said Robert Spitzer, an expert on presidential vetoes who has written about President Bill Clinton's failed effort to use a line-term veto. Spitzer said Clinton used the line-item veto on 10 bills and about 80 different provisions in 1997 before the Supreme Court ruled it was unconstitutional in the 1998 case Clinton v. City of New York.