What will it take to get him either to 65+% disapproval or to 30% or lower approval?
An economic meltdown, a disaster of foreign policy going badly, or a messy war.
President Trump is incompetent to handle normal times, and he can get little done with majorities of the GOP in both Houses of Congress and in most state legislatures. He has offended many of those who voted for him.
So consider an analogy to Jimmy Carter: Carter ran as a Southern good-old-boy, what many thought the South after the end of the racial divide on politics. He proved to be something other than a Southern good-old-boy, so to get re-elected he would have had to win big outside the South in states that he never won. Carter did not do that, but Clinton did. That's the difference between 1980 (voters heavily rejecting Jimmy Carter) and 1992 (Bill Clinton winning a raft of states that Carter never won).
Barring a situation in which the President's Party divides, as in 1908, the worst defeats of an incumbent President since the Civil War have been those in which Hoover (1932) and Carter (1980) lost their re-election bids by huge margins, winning only 10% of the electoral votes, and for very different reasons. The common threads between Carter and Hoover were mass disappointments with the results and a charismatic challenger who offered an unambiguous alternative.
