Attorney General Eric Holder said it’s tough to predict what direction Americans will take marijuana laws in the next decade, but he remains “cautiously optimistic” about the success of the ongoing experiments with legalizing recreational weed in Washington and Colorado.

“I think, so far, I’m cautiously optimistic,” Holder told the Huffington Post. “But as I indicated to both governors, we will be monitoring the progress of those efforts and if we conclude that they are not being done in an appropriate way, we reserve our rights to file lawsuits.”

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Washington and Colorado are testing grounds for marijuana legislation – approved in both states by a 2012 ballot initiative – that directly contradicts federal laws. The Department of Justice began relaxing how it handles that tension and issued a set of guidelines in February meant to expand banking access to legal pot shops in the two states.

Despite his optimism, Holder said he didn’t expect marijuana legalization to sweep the country anytime soon. “I think a lot of states are going to be looking to see what happens in Washington, what happens in Colorado before those decisions are made in substantial parts of the country,” he told the Huffington Post.

In addition to Washington and Colorado’s green-light on recreational pot, 20 other states have medical marijuana laws on the books. Maryland joined 15 other states and the District of Columbia Monday when Gov. Martin O’Malley signed legislation decriminalizing marijuana. Those caught with small amounts of marijuana – less than 10 grams – will no longer face criminal penalties. First-time offenders will be fined $100.

Civil liberties advocates hail decriminalization efforts as a crucial first step in mitigating racial discrimination in how drug laws are enforced. From 2001 to 2010, over 8 million marijuana-related arrests were for possession, according to a report last year by the ACLU. Though blacks and whites largely use marijuana at similar rates, the report found a black person is 3.73 times more likely to be arrested for marijuana possession. All marijuana arrests now account for over half of all drug arrests.

Meanwhile, public support for marijuana legalization is through the roof. According to a Gallup poll out last year, a majority of Americans support legalizing weed – a first in the more than 40 years the polling agency has weighed public reaction.

Both Holder and President Obama have admitted to using marijuana when they were young. “I had ‘youthful experimentation’ – I think was the phrase that we were told to use – when I was in college,” Holder told the Huffington Post, referencing the handful of times he disclosed his drug history before confirmation hearings.