No, the new START treaty does not maintain US nuclear capabilities, because the entire goal of the START treaty is to reduce the number of arms produced around the world, and that includes in the United States. In the United States, official must reduce the number of weapons available in order to comply with the terms of the START treaty. Hopefully, other nations will comply as well.
No, the new START treaty does not maintain US nuclear capabilities, because the United States is reducing its production of nuclear weapons with no guarantee that Russia is doing the same. The United States is left in a position that it may not be able to defend itself, because it is publicizing the fact that it is not producing as many weapons, while trusting that Russia is doing the same.