It requires the approval of the United Nations Economic and Social Counsel's Commission on Narcotic Drugs to remove a schedule 1 item from a member countries drug schedules provided the World Health Organization approves any uses as medicinal.

They schedule drugs through Article 6 of our Constitution which makes treaties law of the land. Our ability to change drug laws in the US is outsourced to the UN. It's not a "Republican or Democrat" issue specifically. Though, the prison system that is increasingly private which makes money hand over fist on drug users and pushers certainly is an issue either political party could champion and change.