The US is sort-of is the world’s policeman.
There is no credible alternative one, and life without a policeman is not a life of peace. Periods where there has been a hegemon have been much more peaceful than ones where contesting powers fight it out.
Life under a Russian or Chinese policeman would not, in my view, be preferable. The UN is the epitome of realpolitik not its repudiation, and is in any case weak.
For all its faults, the US is the most humane superpower there has ever been, sees itself as at least somewhat (imperfectly) bound by norms and laws, and works (typically) in coalitions that are based partly on shared interests but mostly (and imperfectly) on shared values. Those values include the worst-except-all-the-alternatives-ever-tried hits including democracy, human rights, free markets and liberalism.
I dislike Trump becuase he’s weakening the US’s role as a fair-ish an effective-ish world policeman.
Those who oppose him because he hasn’t packed up the US’s bags altogether should be extremely careful what they wish for.