Nearly half a century ago, Richard Nixon called for an "all-out offensive" on drug abuse. It was the opening salvo in America's longest running war.

Successive presidents took up the call to arms. Arrest rates soared and mandatory minimum sentences sent young men - particularly black men - away for long stretches for low-level offences.

Then as violent crime rates fell under George W Bush and prisons became clogged, prosecutions eased. The war on drugs fell out of fashion. Barack Obama called it "unproductive" and sent memos guiding prosecutors away from pursuing low-level offenders.

Now a new administration looks set to turn back the clock. Attorney General Jeff Sessions likes to reminisce about the aggressive law enforcement of the 80s and 90s and recently labelled cannabis "only slightly less awful" than heroin.

[For more of this story, written by Joel Gunter, go to http://www.bbc.com/news/world-us-canada-39623671]