Steven Nelson, U.S. News & World Report

The House of Representatives voted early Friday morning to ban the Department of Justice from spending money to combat medical marijuana in states that allow it.

The fate of the proposal, offered as a spending bill amendment by Rep. Dana Rohrabacher, R-Calif., and 11 colleagues, was uncertain ahead of the vote, with many backers cautiously pessimistic about its chances.

The amendment won surprisingly strong approval in a 219-189 vote that blurred party lines.

Forty-nine Republicans voted for the amendment and just 17 Democrats - including Democratic National Committee Chairwoman Debbie Wasserman Schultz - voted against it.

Marijuana’s previous high-water mark in the House came April 30, when 195 members voted to allow doctors at the Veterans Administration to discuss the drug as medicine with patients. That proposal died with 222 votes in opposition.

The amendment does not make marijuana legal under federal law, but if it survives the Senate and President Barack Obama signs it into law, it would deny the Drug Enforcement Administration and federal prosecutors the ability to investigate, prosecute and incarcerate people complying with state medical marijuana laws.

That may save the federal government millions of dollars and spare patients from the possibility of decades in prison.

"This historic vote shows just how quickly marijuana reform has become a mainstream issue,” said Marijuana Majority Chairman Tom Angell. “If any political observers weren't aware that the end of the war on marijuana is nearing, they just found out."

Dan Riffle, director of federal policies for the Marijuana Policy Project, singled out GOP members for praise.“It is refreshing to see conservatives in Congress sticking to their conservative principles when it comes to marijuana policy,” he said. “Republicans increasingly recognize that marijuana prohibition is a failed Big Government program that infringes on states’ rights.”

In one of this year’s most high-profile medical marijuana prosecutions, a Washington state family of four, plus a friend – nicknamed the Kettle Falls 5 - are facing long prison sentences for growing a garden of pot in a rural area. The five have medical conditions that qualify them under state law to use and grow pot for medical use, but the local U.S. Attorney filed federal charges following a DEA raid.

Attorney General Eric Holder said in August federal prosecutors should begin avoiding charges that carry mandatory minimum sentences for nonviolent drug crimes, and his department has issued guidelines urging restraint from busting medical marijuana patients - but the DEA and some prosecutors have ignored that guidance.

Americans for Safe Access, a grass roots medical marijuana advocacy group, estimated in a 2013 report the Obama administration spent more than $100 million in 2012 going after medical marijuana, part of a three-year spike in enforcement costs. ASA estimated Obama’s Justice Department has spent nearly $300 million combating so far medical marijuana, compared to less than $200 million spent during the entire George W. Bush administration

"No longer will we have to look over our shoulder and worry when the next raid or indictment will prevent us from safely and legally accessing our medicine," said Steph Sherer, executive director of Americans for Safe Access, following the vote. "This is a game-changer that paves the way for much more policy change to come."

Retired Maryland police officer Neill Franklin of the group Law Enforcement Against Prohibition said: "Today marks the beginning of a new era in marijuana policy reform. Never before has the U.S. Congress acted so decisively to protect states' rights to make their only laws regarding marijuana.”

Medical marijuana business people are also excited.

Derek Peterson, CEO of Terra Tech, a company that aspires to grow medical marijuana across the country, said “it's great to see Congress begin to respect the views of their constituents and permit states to govern themselves how they see fit."

Marijuana is currently a Schedule I drug under 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.

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. Twenty-two states and Washington, D.C., currently allow medical marijuana for certain illnesses. Several others have older, unenacted laws allowing doctors to prescribe it, and a handful of states recently legalized more limited cannabis-derived treatments.