*Colorado and Washington became the first states to legalize recreational marijuana in the prohibition era on Tuesday, while medical marijuana was legalized in Massachusetts, putting huge dents into the nation’s war on drugs and signaling a shift from decades of policies that cost $1 trillion in tax dollars over 40 years, led to the arrest of 850,000 Americans for marijuana law violations in 2010 alone, and fueled the rise of deadly drug cartels abroad, reports the Huffington Post.

But even as pot reformers celebrated their long-sought victories, the threat of a confrontation with the federal government loomed. Both ballot measures would legalize recreational marijuana use only for adults, and cannabis would remain a controlled substance under federal law.

In Colorado, Amendment 64 won with 54 percent of the vote in favor to 46 percent opposed. The measure allows the cultivation and sale of marijuana. In Washington, Initiative 502 carried the day with 56 percent of the vote in support and 44 percent against with half of precincts reporting.

Oregon was the lone state where legalization appears to have lost, with 55 percent of voters opposed. Support there may have been hamstrung by the public profile of Measure 80′s primary backer, pot entrepreneur Paul Stanford, who was charged with failure to pay state income tax in 2011.

The successful pro-pot campaigns prominently featured the voices of law enforcement officials who testified firsthand about the corrosive impact of the war on drugs. There was no reason to prohibit marijuana, they suggested, when far more destructive drugs like alcohol were legal.

Elsewhere in the nation, voters sent mixed messages on marijuana for medical use. Massachusetts legalized medical marijuana by a wide margin, becoming the 18th state to do so. The state of Arkansas, however, failed to become the first in the south to allow cancer patients and others to relieve their pain with cannabis.

But there was reason for pause about marijuana reform as signs emerged that the Justice Department could move to block key elements of the ballot measures like tax collection. On Sunday, a former senior adviser to the Obama administration’s Office of National Drug Control Policy, Kevin Sabet, told NBC News that “once these states actually try to implement these laws, we will see an effort by the Feds to shut it down.”

In both Washington and Colorado, action from the Justice Department could jeopardize marijuana tax revenues meant for state treasuries, a key element of selling legalization to undecided voters.

“Our work in Colorado and Washington is not yet done,” said Tom Angell, spokesperson for Law Enforcement Against Prohibition. “We still need to work on effectively implementing these laws … so that we can show that when you legalize marijuana, the sky doesn’t fall.”