It's an important question for both Trump and his opponents, obviously, so both sides have people making estimates.
The findings I've seen are pretty consistent: The majority of Trump's supporters will not abandon him, no matter what. But there are some whose enthusiasm might dip and keep them home on election day. Not many will cross lines. Some, but not many. The most common number is seven. Take his approval rating and subtract seven points if there is a recession. That is not huge, but it would make it very difficult for him to win.