When? Because there was a famous incident when y'all misquoted him as saying he would when he didn't but other than that he's consistently said he's not a fan of the idea.
And quite apart from anything else, I don't see how he possibly could. Even if he somehow lands a Democratic supermajority in Congress someday, the Democratic party does not vote with enough conformity to give him that kind of power. Democrats famously just do not vote in that kind of block.