That is the answer to your question.
The first veto ever made was on Constitutional grounds.
You made a post earlier that said the article didn't represent everything the President said was accurate. I agree with that.
He's angry that he was personally attaked by a campaign ad. Here's more from the letter that I clipped that Jefferson quote from:
"Nor does the opinion of the unconstitutionality, & consequent nullity of that law, remove all restraint from the overwhelming torrent of slander, which is confounding all vice and virtue, all truth & falsehood, in the U. S. The power to do that is fully possessed by the several State Legislatures. It was reserved to them, & was denied to the General Government, by the Constitution, according to our construction of it. While we deny that Congress have a right to control the freedom of the press, we have ever asserted the right of the States, and their exclusive right, to do so. They have accordingly, all of them, made provisions for punishing slander, which those who have time and inclination, resort to for the vindication of their characters. In general, the State laws appear to have made the presses responsible for slander as far as is consistent with its useful freedom. Inthose States where they do not admit even the truth of allegations to protect the printer, they have gone too far."
Just because the President is upset about an attack ad that was presented late in the campaign, is no reason to sign into law legislation (he himself admits is constitutionally questionable) that would prevent it.
Are we going to debate the meaning of "no" as in no law?
Ah, that wasn't an ad. That was a whole web site set loaded with lies.