40% is an extremely low approval rating in a two-party electoral college system like the US.

In the US, each election is only really decided by 10% of non-partisan Americans, who live in the swing states.

90% of other votes don't matter, because those are permanently blue or permanently red states, and they cancel each other out.

So for Trump to lose 10% of Americans would mean to lose 100% of people who decide election outcomes.