10 November 2020 :

Joe Biden has promised to end private prisons, cash bail, minimum mandatory sentences, the death penalty, and reduce the prison population by more than half. 
Here's the expert opinion on what Biden can actually do. 
After “Black Lives Matter”, police reform dominated the debate in the country. But Biden has direct power only over the FBI and other "minor" security agencies. 
The United States has approximately 18,000 "local" police forces, all with their own regulations. Biden could do no more than offer financing to those who apply new methods or cut them to those who do not. 
This "economic" strategy has worked in the past, but today only 3% of the government budget goes to local law enforcement, so enforcing changes with this system is not easy. 
Biden could reactivate a monitoring system on law enforcement misconduct that Trump had blocked. It would need the support of Congress to set a national standard for the use of force. In Congress the Democrats are in the majority in the House, but the Senate is in the balance, and only after a ballot on January 5 will it be known whether the current situation will unblock. 
Biden promised to "reduce juvenile imprisonment to almost zero". 
Trump has dismantled a series of protections provided for minors. Biden will propose that minors' criminal records be wiped, will ban minors from being detained in adult facilities, and will fight arrests for so-called "status crimes": crimes that would not be such if one were an adult, such as drinking alcohol, and school truancy. 
As for the death penalty, Biden can repeal it from the federal system (and only from that) if Congress votes a law to that effect. Trump had forced the resumption of federal executions, stopped for 17 years, having carried out 7 in a few months. A new attorney general could stop them. Biden could, some say "should," go further, and proclaim a moratorium on federal executions, which Obama has repeatedly promised but never did. Such a symbolic action would influence the abolitionist processes taking place in several states. 
Biden would like to end cash bail, which he called a “modern prison for debtors”. But the President has little direct influence on bail, since it is rarely used in the federal system. 
It could ask Congress to pass laws that offer subsidies to states to adopt alternatives. Vice President Harris had proposed a similar law in 2017. 
Biden would eliminate mandatory minimum penalties. Since 1984, Congress has passed dozens of "emergency" laws that, by preventing judges from applying mitigating circumstances, set penalties for a wide range of crimes. Tens of thousands of people are serving very long federal sentences, including life imprisonment, for crimes that today's sensitivity considers "minor". Biden and Harris have vowed to stop this mechanism, and to review backward convictions, especially those for "non-violent drug offenses". 
Biden and Harris are against private prisons. However, Trump, shortly before the end of his mandate, renewed many of the contracts with private companies for 10 years, contracts that would be difficult for Biden to rescind. The alternative is "leave those beds empty". Detention centers for illegal immigrants are also often entrusted to private individuals. Reducing the number of "normal" and "immigrant" detainees is possible but, experts say, could have a significant "political cost". 
More generally, Biden has pledged to allocate 20 billion dollars to invest in favoring prevention over repression. The idea is to grant funds only to states that create "proven and effective" social prevention programs.