Steven Nelson, U.S. News & World Report

President Barack Obama said in December 2012 his administration had “bigger fish to fry” than legal recreational marijuana in Colorado and Washington. But some members of his Department of Justice have continued to wage war on medical marijuana in states that allow it.

That would end if a bipartisan amendment to a spending bill is adopted by the House of Representatives and ultimately becomes law. 

Six Republicans and six Democrats, led by Rep. Dana Rohrabacher, R-Calif., are seeking to ban the Department of Justice – which includes the Drug Enforcement Administration and federal prosecutors – from using funds to go after medical marijuana in places where it's allowed by state law.

Floor debate on the spending bill begins Wednesday evening. The amendment may come up for a vote late Wednesday or on Thursday.

A similar amendment was defeated by a vote of 262-165 in 2007.

But reformers sense momentum. In the closest medical marijuana vote to-date, 195 members of the House – including 22 Republicans – voted April 30 to allow doctors at the Veterans Health Administration to discuss marijuana as medicine with patients without institutional penalties. That effort was defeated, with 222 members voting against the proposal.

Rep. Sam Farr, D-Calif., said following that vote some members changed their minds and some supporters were absent.

Demonstrating the shifting inclinations of Congress, one of the 222 “no” votes, Rep. Morgan Griffith, R-Va., introduced a bill to remove barriers to doctors prescribing marijuana. He told U.S. News he believes pot should be available at pharmacies and covered by health insurance, but said he was concerned about inviting VA doctors to break the law.

National polls show overwhelming support for legal medical marijuana. CBS News gauged support at 86 percent in January and Fox News found 85 percent support in February 2013.

“I think the tables are turning, I’m trying to be optimistic that Congress can act consistently with the popular support for this issue,” says Kris Hermes, a spokesman for the grass-roots medical marijuana advocacy group Americans for Safe Access (ASA).

ASA estimated in a report it released last year that the cost of federal enforcement against medical marijuana was more than $100 million in 2012, part of a three-year spike in the cost of investigating, prosecuting and incarcerating people who comply with state laws. The group estimated Obama’s Justice Department had thus far spent nearly $300 million combating medical marijuana, compared to less than $200 million spent during the entire George W. Bush administration.

“We welcome any clarification or correction that the Justice Department would like to make to our numbers,” Hermes says.

In one of the most high-profile recent prosecutions, the so-called Kettle Falls 5 – a family of four, plus a friend – are facing long federal prison sentences, including mandatory minimums. The five have medical conditions that qualify them to use marijuana under Washington state law, and admittedly tended a pot garden in a rural area.

The eldest of the five defendants, 70-year-old Larry Harvey, joined Farr and Rep. Paul Broun, R-Ga., near the U.S. Capitol on May 7 for a news conference. He cheerfully told reporters about how his wife cooked marijuana cookies, which he ate to alleviate severe knee pain.

Attorney General Eric Holder said in August federal prosecutors should begin avoiding charges that carry mandatory minimum sentences for nonviolent drug crimes. But the U.S. Attorney for the Eastern District of Washington and others are not bound by that guidance.

ASA is asking supporters to contact their member of Congress ahead of the amendment vote.

“We’re close, we’re definitely within striking distance,” says Mike Liszewski, ASA’s government affairs director. “There’s a growing number of members who have constituencies that are directly affected.”

Twenty-one states (soon 22) and Washington, D.C. have legalized medical marijuana, beginning with California in the late 1990s. Others states have dated laws allowing doctors to write prescriptions for marijuana that have not taken effect, or have recently legalized more limited cannabis-derived treatments.

Marijuana is listed as a Schedule I drug by the Controlled Substances Act of 1970, meaning it has a high potential for abuse and no accepted medical value. Obama has resisted calls to administratively reschedule the drug – which he has the power to do – and legislative attempts have thus far stagnated. Doctors cannot prescribe Schedule I drugs, so states that allow marijuana for medical use instead allow doctors to “recommend” it to qualifying patients.

Rohrabacher’s amendment lists 28 states and D.C. by name as exempted from federal enforcement against medical marijuana laws. His 11 co-sponsors are Farr, Broun and Reps. Justin Amash, R-Mich., Earl Blumenauer, D-Ore., Steve Cohen, D-Tenn., Barbara Lee, D-Calif., Tom McClintock, R-Calif., Jared Polis, D-Colo., Steve Stockman, R-Texas, Dina Tius, D-Nev., and Don Young, R-Alaska.