In this case some parts of the economy are failing (or in 'recession') directly due to the president's actions regarding the trade war. Whether these are actually indicative of a macro economic change is debatable I'd say, but soy profits have fallen, for example, and that industry's failure is a direct result of the tariffs.

while i’m on the side of “we have an economic system that crashes all by itself” i would have say though that certain policies of presidents (and the congress) can worsen them, such as repealing glass-stegal (2008 housing crisis) or other financial deregulation (1980s savings and loan crisis)

lots of fun reading:

https://en.wikipedia.org/wiki/List_of_economic_crises

This president has had a lot of influence on the world economy with his erratic behavior towards China, the middle east, and even loyal trading partners in Europe. As a result, we're now in a trade war that nobody needed or wanted, there's a lot of uncertainty around Afghanistan, North Korea, and Iran, etc. This goes beyond the normal ebs and flows of the economy. If anything, it's amazing how resilient the world economy is against that all of that.

The president, any president, does have the power to affect all corners of the economy. The tax overhaul is a good example, that affected everyone to some extent. I do not think anyone is saying the entirety of the economy is based on his policy but there is no question he can move the needle.

The state of the economy has a strong influence on presidential elections regardless of whether it actually makes sense as metric to judge a candidate

Anecdote: I have seen my shares of stock dip by up to 5% because of his tweets.

Is that after they went up because the US markets have been pretty decent the last few years...