A new poll shows that even liberals won't support the measures that will end mass incarceration

While most Americans believe too many people are held in US prisons, they don't support policies that would make a signficant dent in mass incarceration, a survey of 2,000 people by Vox and Morning Consult released Wednesday found.

A whopping 78% of respondents favored cutting sentences for low-risk, nonviolent offenders, but just 29% said low-risk, violent offenders should be let out of prison earlier.

The poll found that the majority of voters - particularly liberals - think mass incarceration is caused by lengthy sentences for nonviolent drug offenders, which may account for their support of cutting sentences for such offenders.

That's not the case, however.

Just 21% of America's prison population is made up of nonviolent drug offenders, while nearly 40% have been convicted of violent crimes, according to data from the Prison Policy Initiative.

Experts and criminal justice reform advocates have become more vocal in recent years about rethinking America's approach to sentencing violent crime, arguing that addressing drug policies alone will not solve mass incarceration.

The poll's results imply a significant challenge for lawmakers: attracting public support for sentencing reform efforts could be difficult.