There are reasons to be skeptical of this alleged quote by Ehrlichman.
As user GatorD42 pointed out when this was brought up before:
>...Baum claims Ehrlichman said that to him in 1994 while he was researching for a book he published in 1996 about the drug war. He didn't include the quote in that book, but instead published it in 2012 and again in 2016, after Ehrlichman had died (in 1999).
If the quote was actually said by Ehrlichman, it doesn't actually describe the drug polices of the Nixon administration. While Nixon is remembered for "war on drugs", the actual substance of his policies seem to be different than what people think it was:
>...I have been fortunate over the years to discuss the distorted memory of Nixon's drug policies with almost all of his key advisors as well as with historians. Their consensus is that because he was dramatically expanding the U.S. treatment system (by 350% in just 18 months!) and cutting criminal penalties, he had to reassure his right wing that he hadn’t gone soft. So he laid on some of the toughest anti-drug rhetoric in history, including making a White House speech declaring a “war on drugs” and calling drugs “public enemy number one”. It worked so well as cover that many people remember that “tough” press event and forget that what Nixon did at it was introduce not a general or a cop or a preacher to be his drug policy chief but…a medical doctor (Jerry Jaffe, a sweet, bookish man who had longish hair and sideburns and often wore the Mickey Mouse tie his kids had given him).
There are a lot of mundane things keeping it going, but sometimes a little bit of conspiracy ends up being right.