This is actually going to be a much shorter post than I thought.
First, I recommend reading this article, which details how Alabama's governor recently resigned.
Note that the margin is 42%-54% which is a ratio of 1.2857, (54/42) which I will express as "as 28.57% ratio lead"
When Trump's disapproval ratio among both Republicans reaches 25%, he will be removed from office by Congress.
Trump could be removed at a lower rate, but by the time it reaches 25%, he's certainly gone. Given how divisive Trump his, this means you'd likely see an approval similar to above, 42%-54% among Republicans, which, probably would be around 20% nationwide.
TLDR; What would it take to remove Trump from office? 80% disapproval.