Laws establishing mandatory minimum prison terms for specific offenses have chipped away at the parole boards' release powers in 40 States; the most extreme expression of this trend is the life-without-possibility-of-parole sentence, which has become law in 21 States. Still, 32 States retain parole boards with the power to release most inmates after a third to a half of their sentences, and 8 States have boards with the power to release most inmates at any time after their imprisonment. Part of the reason for the continuing survival of parole appears to be that the sentencing systems that have replaced it have not necessarily proved to be any fairer, more predictable, or less confusing, as many proponents of parole abolition had hoped they would be. Also, during a time of exploding prison populations, lawmakers are fearful of closing off the parole option for use as a safety valve. Others note that eliminating the parole board as one of the discretionary bodies affecting sentence lengths has simply shifted more discretionary power to judges and prosecutors, particularly prosecutors, who determine the charge under which sentencing will be imposed upon conviction. This narrowing of discretionary decisionmaking affecting sentencing is viewed by many to be less desirable than having another discretionary body, the parole board, involved in tailoring ultimate sentence lengths to the individual offender.