There is also the issue of the Americanist Heresy, which the author may be promoting, possibly unknowingly.
While I'm not sure I know what is meant by the "Americanist Heresy," I will note that the artist here is represented as saying that "[i]n my painting I used the 'Da Vinci - Last Supper' to represent the Covenant our Lord has made with the people of this land." There is no scriptural support for such a statement, which is surely incorrect, if not altogether heretical.
The only nation that has been in a corporate covenantal relationship with God is Israel -- i.e., the Jews. God has made no "covenant" with the people of the United States. To the extent this painting is meant to communicate that such a "covenant" exists or has ever existed, it is idolatrous nonsense.