A recent 8th Amendment case in the United States Court of Appeals for the 7th Circuit was unexceptional, but does provide a good summary of 8th Amendment case law in non-capital cases.
The case involved an 8th Amendment cruel and unusual punishment challenge to a federal 15 year mandatory sentence for a man convicted of distributing child pornography over the internet while on parole for child molestation. The sentence was upheld as constitutional under the 8th Amendment. As a legislator, I would have set a lower mandatory minimum for that crime (although it isn't clear to me that he would deserve a minimum sentence if the minimum was lower), but, given his criminal history, parole status and the legitimate argument that distributing child pornography is much more serious than distributing other kinds of pornography, it is hard to argue that this comes anywhere close to the showing of disproportion that precedent has held is necessary to show cruel and unusual punishment based on the length of a prison term imposed in a non-capital case. The fact that there was no plausible argument in his case that he didn't believe that it was genuinely a depiction of a child rape produced for commercial purposes, and the fact that he was subject to far more strict limits on this kind of behavior than the general public, given that he was on parole for a child sex offense at the time, also mitigates any concern that the criminal child pornography statute was unreasonably broad as applied in his case. As the 7th Circuit accurately rules, the sentence is harsh, but not unconstitutionally so.
But, I provide the link above to the ruling, because the case provides a succinct and accurate statement of the law of cruel and unusual punishment in cases involving long prison sentences from minor crimes (the opinion runs to just 8 pages, and the summary of the prevailing law is just a couple of pages long). Prevailing under the 8th Amendment in such a case, under current law, is virtually impossible. The only case where a criminal defendant has been successful in making such an argument involved someone sentenced to life without possibility of parole for writing a $100 no account check (and for having a moderately long history of non-violent crimes). This general background precedent is, unlike this particular case, a travesty.