WASHINGTON (AP) — It's easy for Congress to meddle with the District of Columbia's decision to legalize recreational use of marijuana, but taking on the states is a different matter.

A massive, catch-all spending bill Congress passed last week contains a provision preventing the District from using federal money to implement any law or regulation that repeals or reduces marijuana-related penalties. The action is in direct response to a voter initiative passed last month that allows possession of up to 2 ounces of pot or up to three mature plants for personal use.

The Constitution gives Congress the power to review and possibly reject all legislation approved by the District's elected officials or its citizens.

Congress has less leverage with the states, and thwarting efforts supported by a plurality of voters back home could prove politically risky at election time.

"That's sort of asking for a head-on collision with states' rights," said Philip Wallach of the Brookings Institution, a Washington-based think tank.

Wallach said the most ready tool at Congress' disposal in persuading states to keep marijuana illegal would be to withhold money for certain programs if state marijuana initiatives conflict with federal law. That's something Rep. Trent Franks, R-Ariz., the chairman of the House Judiciary constitution and civil justice subcommittee, says he's prepared to support.

Franks said the marijuana legalization movement endangers the nation's youth.

"Unfortunately, it will only deepen this country's drug addiction crises," he said.

But many other Republican lawmakers don't seem ready to take such concrete steps.

Sen. Charles Grassley of Iowa, the likely chairman of the Senate Judiciary Committee in the next Congress, said he's not prepared to say which issues his committee will focus on. The committee has jurisdiction over the Justice Department, which enforces federal drug laws and has said it will not stand in the way of states that want to legalize, tax and regulate marijuana as long as there are effective controls to keep it away from kids, the black market and federal property.

Sen. Ron Johnson of Wisconsin, the likely incoming chairman of the Senate Homeland Security and Governmental Affairs Committee, has said he would like to hold a hearing on how well marijuana legalization efforts are working, but that's as far as he would commit.

Meanwhile, proponents of marijuana legalization know exactly where they want to go next. The itinerary includes pushes into California, Arizona, Nevada, Maine and Massachusetts. There's money to be raised for campaign ads, ballot initiatives to write and petition campaigns to organize. Four states so far —Washington and Colorado were the first, followed by Oregon and Alaska — have voted to legalize marijuana.

The groups are confident that momentum is on their side and that most members of Congress know they can't do anything about it.

"I think everyone knows it's inevitable. Republican Senate or not, we're going to keep moving forward," said Bill Piper, director of national affairs for the Drug Policy Alliance, a nonprofit organization that advocates an overhaul of drug policy.

The group points to another section of the just-passed spending bill as evidence that most lawmakers don't want Congress to interfere with state decisions regarding marijuana. That provision prevents the Justice Department from using funds to arrest and prosecute medical marijuana patients or distributors who are in compliance with their state's laws.

Twenty-three states have laws allowing medical marijuana, according to the National Conference of State Legislatures.

The GOP's most consistent backer of the legalization movement, Rep. Dana Rohrabacher of California, said he's simply unsure where a Republican-controlled Congress will take the marijuana issue.

"I can't read my fellow Republicans on this. Behind the scenes, they will tell you, 'Oh, yeah, (prohibition) is stupid, but I'm not going to risk my political career,'" Rohrabacher said.

Republican Rep. Andy Harris of Maryland, an anesthesiologist who has led the congressional effort to halt the District of Columbia's marijuana initiative through September 2015, said prohibiting recreational marijuana use is the right thing to do. He's not worried about the politics.

"If we can educate the public about the hazards, especially given the high unemployment rate among D.C. youth, the problems they have in the educational systems, I think we can convince people the last thing they need in the District of Columbia is legalization," said Harris, who represents Maryland's Eastern Shore.

When asked whether Republican leaders were ready to take on the legalization trend elsewhere, Harris said he would agree the issue is not a top priority for them.

"The plate of leadership is so full with foreign affairs and economic matters in this country, this is just not on their radar screen and appropriately not on their radar screen," Harris said.

Brookings' Wallach said GOP leaders have a good grasp of what their constituents care most about.

"Even the folks that really haven't changed their mind too much (on legalizing pot) at least have to re-evaluate the politics, and say, 'Does going after this from a strong enforcement angle make any political sense?'" Wallach said. "It probably makes political sense for a lot of people to just lay low on this issue."

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