Let's imagine a state signs this and is a tipping point state for the presidential election. If this compact has any effect, it will be for the state's electors to vote against the popular vote in that state, resulting in the election of the undesired president according to the state's voters.
Nothing wrong with that constitutionally, but I suspect the politicians will feel differently after the voters express their opinion of the matter.
Yes, of course. If you support the election of President based on national popular vote, then you surely realize that sometimes the President will not be the candidate that was preferred in certain states.
If this actually does pass the tipping point, nobody will even be counting electors any more, they will only be counting the popular vote. The electors will be considered just a formality.
Well, yeah, people who don't like the winning candidate will be upset. Perhaps some people will be upset that the preferred candidate in their household, neighborhood, city, county, or state didn't win. I don't see how this is an effective argument against this policy.
The US constitution says that presidential electors are chosen in a manner prescribed by the state legislature. They change the prescription, just as some have changed it now.
Nothing wrong with that constitutionally, but I suspect the politicians will feel differently after the voters express their opinion of the matter.