[SAJ]

Fiddlesticks. Where is it etched in granite that a 'compact' must be written down?

The very fact that these states are and have been for some time discussing this among themselves makes it a compact.

You and I, or any two other parties, can very easily make a compact, at law, by simply agreeing verbally that we both shall do such-and-so at some future time under some set of conditions.

[thefrankbaum]

But if States discuss among themselves how to define murder, or how to treat commercial transactions (see: UCC), and then all adopt the same law, it isn't a compact. This piece of legislation does not govern any interplay between the states, and thus is not a compact.

Electors are chosen in the Manner as the Legislature of the State may direct. If every State passed a law allotting their electors based on the results of a single coin flip, it would be Constitutional. As CJ Roberts said, there are plenty of bad ideas which are Constitutional.