The way the multi-state pact works is that member states agree to give all their electoral votes to whoever wins the national popular vote, regardless of who the state actually voted for.
It doesn't actually get rid of the Electoral College, that would take a constitutional amendment, it just re-apportions the Electoral College votes based on the outcome of the popular vote.
So in 2000 and 2016, the Democratic candidate won Oregon, and won the popular vote, they would get all the electoral college votes, not a problem, even though they lost the election overall.
Where it WILL be a problem is if the Democratic candidate wins the state, but the Republican candidate wins the national popular vote.
State voters will be told "Yeah, we don't care who you actually voted for, the Republican gets the votes from your state." OMG there will be riots.
Think of it like this... Your vote in your state gets inverted because of voters in Texas, Oklahoma, Louisiana, etc. etc.