“John McCain is right on that one. The line-item veto is the best tool the president has to rein in excessive spending.”

In attacking former New York City Mayor Rudy Giuliani for successfully challenging the line-item veto in court, Mitt Romney asserts that the veto is a great way to cut spending.

He says he used it more than 800 times as governor of Massachusetts. More than 40 governors have the power.

But calling it “the best tool” for a president to cut spending is saying too much. In fact, federal budget experts are in some disagreement over how well a line-item veto would work if the power was restored to the president.

President Clinton was given the power by Congress in 1996. It was declared unconstitutional in 1998. During the time that he had it, the so-called “pork barrel” special interest projects and targeted tax benefits he vetoed would have saved about $600-million over five years.

The Congressional Research Service pointed out that for budget year 1998, the savings were about $355-million out of a total budget of $1.7-trillion.

Congress would have to amend the Constitution to give the president the same power Clinton had. Short of that, Congress could give the president a limited power to rescind spending and force the House and Senate to vote on those proposed cuts. Currently, Congress can ignore presidential requests to rescind money.

Budget analysts aren’t sure what impact the line-item veto would have. “To the extent that the line-item veto act shifts power from the Congress to the president, it may change behavior in subtle ways that are difficult to observe,” June O’Neill, then-director of the Congressional Budget Office, testified before the House Rules Committee on March 11, 1998.

Louis Fisher of the Congressional Research Service agreed, writing in 2005 that as a result of deal-cutting over use of the veto between Congress and the White House, spending could actually increase. Fisher’s idea is that in the reshaping of power between Congress and the White House that would occur with a line-item veto, presidents could barter for extra spending in areas they favored in exchange for letting other projects go unvetoed.

It’s this fuzzy picture that keeps us from going any further than Half True on Romney’s claim that a line-item veto is “the best tool” for a president to cut spending.