Everyone comes down from these highs. But Trump is starting with dramatically lower marks than any recent predecessor.
This is not surprising. During the campaign and even in the exit polls, a large number of his own supporters thought Trump was unfit to be president. He won with 46% of the vote and even a substantial number of supporters had a deeply negative view of him. 41/40 is sort of respectable by that measure.
But it all adds to the mammoth instability of the moment. You have a president-elect breaking at every turn elements of long established practice, upending alliances and diplomatic understandings which have undergirded peace in different parts of the world for decades. He's picking a cabinet made of plutocrats campaign donors, a few conventional rightwing nominees and appointees but lots of people who are manifestly unqualified for their posts. And all this comes with public approval ratings which would be near the danger zone at any point in a president's term.