I think they need 67 votes to override, not 66, but I could be mistaken.
If he approve he shall sign it, but if not he shall return it, with his Objections to that House in which it shall have originated, who shall enter the Objections at large on their Journal, and proceed to reconsider it. If after such Reconsideration two thirds of that House shall agree to pass the Bill, it shall be sent, together with the Objections, to the other House, by which it shall likewise be reconsidered, and if approved by two thirds of that House, it shall become a Law. But in all such Cases the Votes of both Houses shall be determined by Yeas and Nays, and the Names of the Persons voting for and against the Bill shall be entered on the Journal of each House respectively.
66 is just short of two thirds of 100.
If Trump doesn't sign this, he'll not only elevate this story to the top, the antiRKBA children's march and naming of Bolton will be forgotten news!