Although the Obama-Biden administration made strides in shrinking the prison population, Biden's estimate is exaggerated.
From when Obama-Biden took office in 2008 to when they exited in 2016, there were about 9,500 fewer inmates, according to the Federal Bureau of Prisons data. A Biden spokesperson told Factcheck.org last year that the presidential candidate got the 38,000 figure from a 2018 ACLU letter which measured the data from a high-point figure in 2013, when there were over 219,000 federal prisoners. But that failed to account for the fact that the number of federal prisoners rose in Obama’s first five years in office.
By 2016, Obama helped bring the federal prison system to its lowest population size since mid-2004 and its lowest incarceration rate since the end of 2002, according to the Washington Post. Another study by Pew Research claims the number of sentenced prisoners in federal custody fell 5 percent i.e., 7,981 inmates between Obama’s first year in office and 2015.
The number of inmates has continued to decline under President Donald Trump, according to Factcheck.org. As of February this year, there were over 175,000 federal inmates, a little over 17,000 fewer than in Obama’s last year in office.
Therefore, although the Obama-Biden administration made strides in shrinking the prison population, Biden's estimate is exaggerated and hence we mark this claim as partly true.