Question

​when voters adjust their long-term allegiance from one party to another in response to ideological changes, it is referred to as

Answer 1

I believe the correct answer is realignment.
They are realigning with another party so as to accommodate their new ideological views which fit better with that second party they want to vote for instead of the old one they used to vote for many years. It happens when there are drastic changes in both the party and the voters themselves.