Russia and USA are two by far the biggest nuclear weapon powers and their future is highly merged (as in the title of this post) to define the future of mankind. So, the stability of this duet is important for all of us. US presidential elections may create catastrophic turbulence and increase the probability of major nuclear war in case the US power will be not well defined. This might happen if the outcome of the elections is not accepted by the losing party.
1. most dangerous is the case when Trump loses and does not recognize the loss.
2. if Biden loses and does not accept the loss - the major control is safe for some time but the vacuum of power may increase dramatically
3. If Trump wins and Biden accepts or vice versa the overall stability may be retained for some time. But the battle may not end worldwide.