Well, how about a worldwide pandemic that has killed more than 400,000 Americans (and far more in the rest of the world) and its attendant economic problems? The pandemic was Trump's moment to shine as a leader, but instead, he pulled us out of WHO, denied the severity of the problem, disdained common sense measures to contain it (masks, social distancing and contact tracing), touted measures not supported by science, appointed people who know nothing about epidemiology (Azar, Pence, Kushner) to lead the response and fomented distrust towards actual scientists and doctors.
On the bright side, he did get more respirators into use and he did encourage the vaccine development (although the US was not the first to get it done).
As to the OP, unity cannot be unilateral. If the other side is adamant about opposing every action, there is not much that can be done.