Once the USA has a sane commander-in-chief again, it's going to need to completely overhaul its approach to the Eastern European region, among other things.
There are serious constraints on what can be done. Among others, why would any other country make an agreement with the US where the payoff is more than 4 years out? It has repeatedly demonstrated an inability to keep promises.
The JCPOA (more commonly known as the Iran deal) constrained Iran's nuclear program, and it was with great disappointment that I watched the administration withdraw. But there were anecdotal reports of transgressions on Iran's part, and the JCPOA was never submitted to the US Senate for ratification, which means it was never a legally binding agreement under U.S. law. Like the Paris climate agreement (most of its signatories saw their GHG emissions increase, but not the US; so much for the effectiveness of such agreements to achieve concrete progress in the fight against climate change).