A Democratic U.S. senator is asking the federal government to take this remarkable step: completely ban Bitcoin. Sen. Joe Manchin of West Virginia sent a letter today to the Treasury Department, the Federal Reserve, and other regulators characterizing the virtual currency as encouraging “illicit activity” as well as being “highly unstable and disruptive to our economy.” Manchin, who is a member of the Senate banking committee, suggested in the letter — titled “Manchin Demands Federal Regulators Ban Bitcoin” — that a complete prohibition was appropriate because Thailand, China, and South Korea have already enacted severe restrictions or bans of their own. It’s unlikely that the Federal Reserve and the executive branch possess the authority to prohibit Bitcoin without a new law enacted by Congress and signed by the president — making Manchin’s letter something of a publicity stunt.