Is National Popular Vote Interstate Compact Constitutional for electing POTUS?

[pbrower2a]

Any compact must represent something. There are methods of allocating the electoral votes of a State that would never pass Constitutional muster. "All and only votes by persons of the Caucasoid race" is the most obvious.  The choice of the sitting Governor is obviously despotic in nature. A vote by a state legislature gives powers to states that the Founders never thought appropriate (and that probably applies also to gerrymandering that gives one Party's nominees a built-in advantage). A coin flip would be unduly arbitrary.

Dividing states by Congressional districts is only as good as the geographic basis. Maine is now homogeneous enough that hardly any division of the popular vote by district would happen. Nebraska at the least seems to split neatly into well-defined regions. Gerrymandering to establish a large number of slightly-R-favoring districts and that few districts have huge pluralities of D voters as has happened in Pennsylvania, Ohio, Michigan, and Florida  can ensure the dilution of votes of what might otherwise be a majority.