"The Obama administration on Thursday said it would not sue to undo laws legalizing marijuana in 20 states..."

"... although it will monitor operations in those states to make sure they do not run afoul of several enforcement priorities."

In a memo sent to federal prosecutors nationwide on Thursday, James M. Cole, the deputy attorney general, laid out eight priority enforcement areas. They are aimed at preventing marijuana sales to children, illegal cartel activity, interstate trafficking of marijuana, and violence and accidents involving the drug.

But:

Last week, the White House said President Obama did not support changing federal laws regulating marijuana, which treat the drug as a highly dangerous substance with no medical purpose.