The president has a sort of negative power in that he can sometimes *refrain from doing things*. But he can't really *do things*.
The president can theoretically prevent a war from breaking out.
Although he must be strong willed, intelligent, and willing to challenge his "advisors" as JFK did multiple times, to avoid war, because if they really want a war, all they have to do is bring in some unnamed guy from CIA and he will say oh we noticed they are moving nuclear missiles into place at this area, we discovered some bioweapons lab with anthrax, they are unplugging babies from incubators, whatever, and 99% of politicians will believe this and just go to war.
But as far as having actual power to *do* things, the president has little to no power.
If President Biden sits down with any world leader at the negotiating table and they try to create an arrangement, the best the president can do is say "Oh well I'll take this to Congress and maybe a year from now we can get 50% of the things I am promising you to happen in the future, until my replacement comes into power and reverses them" whereas someone like Putin or Xi can sit down and make real promises and make things happen.
Anyway, to whatever degree a president has power, America is, how does Lavrov put it? Agreement incapable? You cannot trust even our official policy. Just look at the One China Policy. We openly subvert our own treaties and agreements.