Emissaries and consulates are typically ran by career government employees in the US but their operation is overseen by the Secretary of State (a presidential cabinet member) and the State Department. So the presidential appointee has a lot of power over what does and does not happen at consulates/emissaries.

It's not optimal but it's what we have.

I imagine foreigners in the US must feel awful.

A lot of non-foreigners feel horrible about it being inflicted on people too.

In the end, everything is determined by politicians...

E.g. who appoints Supreme Court judges and has them own them favors or agree to their ideology? Politicians...

Well, yes, politicians are the ones who choose the leadership of the branches of gov't, including the branch that decides on visas.