the loophole they have found is the will still award electoral votes but instead of giving the electoral votes to whoever won the majority of votes in the state they will give all the electoral votes to the winner of the national popular vote
That will dilute (i.e. lessen, or abridge) the votes of that state's eligible voters. For example, consider California which has a population of 37 million. Their voting population represents 12% of the national vote. If California decides to allow the entire nation to select it's electors, then 88% of the right of their voting population had been denied since each California voter would only count as one-eight of a vote. Thus by the 14th Amendment, their basis of representation therein shall be reduced. So California's 63 Representatives are reduced to 8, and their electoral votes are reduced from 65 to 10.
Of course I do realize that since this is actually in the Constitution, it means that Democrats will ignore it.