Good question. There's room for argument of course, but I would say GHW Bush.Here's a simple question. Nothing mean about it. Who was your favorite Conservative president within your lifetime?
My opinion might have change IF he had had 2 terms.
It is accepted that his 1st campaign promise of "read my lips, NO new taxes" torpedoed his 2nd election & I accept that too.
In my mind that is a perfect example for line item veto by the president. Taxes were raised in a bill that had issues MORE important to him than raising taxes & those bills included higher taxes but it was an up or down vote on the entire bill.
The Dems successfully rode that fact of higher taxes in the next campaign.
Clinton was given the line item veto power for a short period until the SCOTUS properly ruled that unconstitutional. It is a little more complex than that but I put it simply.