America's prison boom is starting to fizzle.

For decades, the country had little trouble filling its ever-growing number of prisons, thanks in large part to tough-on-crime policies and harsh drug laws. But a combination of falling crime rates, softer sentences for low-level and nonviolent offenders and a dwindling appetite for hefty prison budgets has begun to whittle away at the number of people behind bars. That is allowing many states to do what a few years ago seemed unthinkable: close prisons.

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