This week Sen. Jeff Merkley (D-Ore.) told Talking Points Memo he is inclined to vote yes on Measure 91, which would legalize marijuana for recreational use in his state. "I think folks on both sides of the argument make a good case," Merkley said. "And there is concern about a series of new products—and we don't have a real track record from Colorado and Washington. But I feel on balance that we spend a lot of money on our criminal justice system in the wrong places and I lean in favor of this ballot measure."

This makes Merkley the first U.S. senator to endorse the legalization of marijuana. [But see the addendum.] Sen. Rand Paul (R-Ky.), whom you might expect to agree with Merkley, so far has shied away from supporting legalizaton, although he has said drug policy should be left mainly to the states. A few more senators, including Pat Roberts (R-Kan.) and Lamar Alexander, have said the federal government should not try to block legalization in Colorado, Washington, or any other state that follows their example. But at this point Merkley is the only senator to openly say that legalization is better than prohibition.

On the face of it, Merkley's status as the Senate's sole legalizer is puzzling, since recent polls indicate that somewhere between 48 percent (CBS News) and 58 percent (Gallup) of Americans think marijuana should be legal. You would think that more than 1 percent of the U.S. Senate would agree by now. The picture is similar in the House, where many members seem to agree with Roberts and Alexander that states should be free to legalize marijuana but very few are prepared to say it's a good idea.

Legislators are much less shy about taking controversial positions on other contentious issues. When it comes to, say, abortion or gun control, there are plenty of senators and representatives on both sides of the debate, even though they are bound to alienate many voters by taking a stand. But on the subject of marijuana, politicians seem terrified of saying anything that could be portrayed as soft on drugs, even when dealing with reforms, such as legalizing medical use, that have had solid majority support for years. Presumably that's because they think prohibitionists are more passionate than legalizers and therefore more likely to vote based on this issue. The only way to really test that hypothesis would be to follow Merkley's lead and see what happens.

In the end, it may not matter that almost no one in Congress is willing to say pot should be legal, as long as enough of them are willing to take a federalist approach to the issue. A legislator could oppose legalization or remain agnostic on the subject even while supporting legislation like the Respect State Marijuana Laws Act, which Rep. Dana Rohrabacher (R-Calif.) introduced last year. Rohrabacher's bill would essentially repeal the federal ban on marijuana, making it inapplicable in states that decide to legalize. That's something that any conservative who pays lip service to federalism should be able to get behind without looking like a pot-loving hippie.

Addendum: Tom Angell points out that Sen. Patty Murray (D-Wash.), who opposed her state's legalization initiative, last March told the Seattle Post-Intelligencer, "I support what voters in Washington state have done." I'm not sure that counts as an endorsement of the policy, since Murray was talking about letters aimed at getting the Justice Department to clarify its position regarding legalization in Washington and Colorado. "I believe my name has been on letters to the Justice Department," she said. It's clear that Murray wants the feds to respect the will of Washington voters; it's not so clear that she has reconsidered the merits of legalizing marijuana. But if we count Murray, that makes two senators who publicly support legalization, or 2 percent of the Senate.