You can't ascertain that something violates the Constitution, until you correctly ascertain the will of the lawmakers at the time they made it. You can't ascertain the will of the lawmakers at the time they made the Constitution, unless you use the methodology of construction the lawmakers probably believed would be used.
Here is an interesting excerpt from Madison's Notes.
Mr. DICKENSON mentioned to the House that on examining Blackstone's Commentaries, he found that the terms,5 "ex post facto" related to criminal cases only; that they would not consequently restrain the States from retrospective laws in civil cases, and that some further provision for this purpose would be requisite.
When Mr. Dickenson ascertained the meaning of the term "ex post facto", he consulted Blackstone's Commentaries for the answer. Why did he do that? Was he following some sort of well established generally accepted methodology of construction?
Should the words in the Constitution be generally understood according to the way Blackstone used them in his Commentaries?
Note: Dickenson had the best training in the common law of all the founders. He also fought for the British during the Revolution.