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Not constitutional!
Also not in accordance with the SCOTUS “one man, one vote” decision.
The states must count votes.
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It is constitutional, provided the states decide to do it by themselves with the collusion of the compact. We do not vote for President, the Electoral College does that. The states don't count the votes. The Electors vote and the Federal Government count the votes. For decades, the general popular vote was known as the "beauty contest". Everyone knew that the real vote was by the electors and the states chose from two slates of Electors. Almost universally for the last 100 years or so, the states chose either the Democrat or Republic slate based on who won the popular vote.