She says that federal prohibition came about not because of the federal government imposing it on states, but because most of the states had adopted policies of prohibitions themselves. With the 1937 Marijuana Tax Act, the federal government simply changed its law to reflect the growing sentiment of the states, she adds.
But there could also be a backlash, she and others say. What happens next, she says, would be determined by how rigorously the federal government fights the trend, and whether the state experiments are deemed a success in terms of a positive outcome with minimal harm.
"Both of these two things are entirely unknown," Ms. Pacula says.
Same-sex marriage. Voters have never endorsed same-sex marriage. Thirty of 31 ballot initiatives to ban same-sex marriage have succeeded, and all attempts to legalize it via the ballot box have failed. But experts will be watching this November to see if Mr. Obama's open declaration of support for same-sex marriage earlier this year has helped shift the calculus.
Maine is attempting to become the first state to legalize same-sex marriage by ballot initiative. It used a popular referendum in 2009 to block a same-sex marriage law passed by the Legislature and signed by the governor. But this year, the initiative is leading 57 percent to 36 percent, according to a September poll by Critical Insights of Portland, Maine.
Washington and Maryland are holding popular referendums on laws legalizing same-sex marriage, which were passed by their legislatures and signed by their governors. A majority of voters in both states support the laws, according to polls.
Meanwhile, Minnesota voters will consider a constitutional amendment defining marriage as between a man and a woman, though it would leave open the possibility of civil unions. Polls show a majority supports the amendment.