In a move that marijuana advocates hailed as a watershed in their fight against cannabis prohibition, the U.S. House voted late Thursday to block the Department of Justice from interfering with state medical marijuana laws.

But legal experts Friday said the vote was more symbolic than practical.

First there is the challenge still ahead: The appropriations amendment that the House approved — which tells the Department of Justice it can’t use any money in medical marijuana states “to prevent such states from implementing their own state laws that authorize the use, distribution, possession or cultivation of medical marijuana” — must also receive support in the Senate.

Even if it does, Vanderbilt law professor Robert Mikos said the amendment’s language makes it unclear how much the Justice Department is actually limited.

“It’s just a can of worms,” said Mikos, who has written frequently about the intersection of state and federal marijuana laws. “Even in the extremely unlikely event that this would ever be litigated, it would be difficult to predict what this means.”

Marijuana advocates, though, said the vote’s significance lies much more in what it says about shifts in pot politics. The amendment passed the House late Thursday by a vote of 219-189. Colorado’s three Democrats voted in favor of the measure; on the Republican side of the state’s delegation, only Mike Coffman did so.

When an identical amendment was offered in 2012, it failed, with only 163 votes in support.

“This is a watershed moment in American politics,” said Aaron Houston, who has lobbied for pro-marijuana causes in Washington, D.C., for the past decade. “It is the first time that the U.S. House of Representatives in the history of the war on marijuana has voted to support some relaxation of marijuana laws.”