There are, in general, two things that can be done about overcrowding in prisons in the United States.
First, we could do what we have generally been doing to this point. That is, we can build more prisons. If we build more prisons, the prisons will no longer be so overcrowded. We could also, as an adjunct to this, try to take political steps to ensure that prisons will not be deemed overcrowded. If we appoint and elect more conservative judges, they might be less inclined to think that crowded prisons constitute cruel and unusual punishment.
Second, we can try to reduce the number of people that we send to prisons. There are two main ways to do this. One would be to reduce the punishments for relatively minor crimes. If we stop incarcerating so many people for non-violent drug crimes, we might reduce the overcrowding. Another would be to have programs that make people less likely to commit crimes. These would include things like better education and job training programs for young people in poor communities. They might also include training programs for people who are in prison so that they might have better chances to get jobs when they are released.
My own inclination would be to reduce the numbers of people that we send to prison, but the problem is that such programs are difficult to devise and do not pay immediate dividends. This can make it very hard to make them politically palatable.