On the other hand, a lot of the "tough on crime" messaging comes from the unique context of the 70s and 80s, when crime was much higher than today and continually rising. I'm hopeful that prison reform is a much more politically palatable message now that crime has been trending down for decades.

Crime may be trending down, but I think the perception is that it's more common - I remember reading the results of multiple polls to that effect over the last decade. People consistently believe that crime has gotten worse. Part of there blame was placed on the news media overreporting crime stories (as what else are they going to talk about when nothing exciting is happening?) which skews public perception of the actual scale of the problem.

The polling I'm familiar with (e.g. https://news.gallup.com/poll/1603/crime.aspx) indicates that there's been a significant shift. In particular I'd point at the "too tough, not tough enough or about right" question; in 1992, the idea that we shouldn't be tougher on crime was quite radical and the idea that we're too tough on crime was practically nonexistent.

That particular question has shifted, sure. But in the early 90s, wasn't crime at historic highs in the country? In any case, it has shifted to the point that only twice as many people believe that we should be tougher on crime rather than more lenient. But look at the chart for the question "Is there more crime in the U.S. than there was a year ago, or less?" It shows that "More" dominates "Less" at around 65% - 20%, and has done so since the turn of the millenium. The majority still believe that crime gets worse, year on year.