Washington D.C. legalizing recreational cannabis the same as alcohol MUST make the ENTIRE NATION legal by default due to the fact D.C. is the nation's FEDERAL CAPITAL, created and only existing as a federal district under the exclusive jurisdiction of the Congress & the District, making it not a part of any U.S. state. The centers of all three branches of the FEDERAL government of the United States are in the District, including the Congress, President, and Supreme Court.
When our elected representatives created and passed legislation that made recreational use of Cannabis legal in Washington, D.C. (for themselves); then that law MUST be extended and recognized nationwide by default for the rest of the U.S. Citizens. What's good for the goose is good for the gander.