As for the politician who won an election with a 98% margin and is down in the 60s in current polls, the first obvious question is “who was the opponent?” Here in Massachusetts we sometimes have elections where the Republican Party doesn’t bother to field a candidate. (Massachusetts is a blue state where Republicans rarely win statewide offices other than Governor… and the Republicans who win that office sometimes aren’t the sort that get elected in the other states. For a prime example, look at what happened to Bill Weld and his national aspirations.) That might leave somebody in an election with no opponent at all, or with only a fringe independent candidate on the ballot, a situation that leads to very large margins of victory. But in the current election they might be facing a real opponent, and people who voted for the incumbent last time because of a lack of a viable alternative may support that opponent.