During his run for the presidency, Barack Obama instilled hope in medical marijuana supporters by pledging to respect state laws on the matter. And for the first two years of his term, he was generally faithful to his promise. Yet suddenly, and with no logical explanation, over the past eight months he has become arguably the worst president in U.S. history regarding medical marijuana. 1. In 1970, Nixon signed into law the Controlled Substances Act, which placed marijuana in Schedule I -- the most…