The party slate of electors are not appointed in the Constitutional sense. They are state party insiders, mostly county chairs and precinct captains who were vetted by the party and the candidate to be included in the slate.
However, those slates are methods selected by the state legislatures in Article II Section 1 of the Constitution. It doesn't have to be that way, it's just the way 48 states have chosen to do it. The Constitution is agnostic to the way the legislature choose to do it, which is why the language of "appointing" is in the Constitution. It supersedes what the states do.
In Maine and Nebraska, where they appoint electors by Congressional district, you can't say that someone is appointed solely by being selected by the party because the whole slate does not go to the Electoral College. If Maine's CD-2 goes Republican while CD-1 and the state's popular vote go Democrat, only the Republican Elector from Maine CD-2 is appointed. You can't say that the entire Republican slate constituted appointment.
What if a state chose to make Electors individually elected in each Congressional district? First, would you agree that Article II Section 1 gives the state legislature the power to select the method such that candidates for Electors can run in each district as separate races? In this case, you might see three or four people in each district run for Elector. You cannot say that a person is appointed yet just because they are running, yet you are saying that by simply being on the candidate's designated slate.
Just for grins, would you say that Article II Section 1 allows state legislatures to decide to make the top citizen property taxpayer in each Congressional district an Elector? In this case, there are no elections, just direct appointments (there's that word again).
The electors aren't considered appointed until they win the election, either as a slate, as a separate Congressional district, as a race all their own, or by direct appointment by the legislature.
-PJ
This is as simple of an explanation as I can find...
The Electoral College
For example...What happens if Puerto Rico, or any of the other territories, becomes a State?
The number of apportioned electors increases because the formula is set!
It's not that hard to understand!
No twisting, no need to take the plain text of the Constiution out of context.
The number of apportioned electors increases because the formula is set!
The new electors are appointed to the new State by that formula.