WASHINGTON — Much of Congress was up in arms when Attorney General Jeff Sessions announced changes last week that opened the door to more federal marijuana prosecutions, undercutting a growing number of states that have legalized the drug for medical or recreational purposes.

But will the GOP-led body defy President Trump's top law enforcement officer? And will prosecutors given them reason to?

One initial test is pending in the coming days, when lawmakers will attempt to pass a sweeping government funding bill — the kind of measure that for years has included bipartisan language barring prosecutors from pursuing cases against medical marijuana use in states that permit the practice.

Some, including New Jersey Sen. Cory Booker, want to make sure that policy is renewed, and perhaps expanded to cover recreational marijuana use.

The so-called Rohrabacher-Blumenauer amendment has been in place — and regularly renewed — since 2014. Its fate is up for consideration again because it is scheduled to expire on Jan. 19, along with the most recent federal spending package.

"Extending the rider that prevents the Department of Justice from interfering in states' ability to set medical marijuana policies really is a no-brainer," Booker, a Democrat, said in a statement to the Inquirer and Daily News. "What's more, Congress should act to pass a permanent law that ends the federal prohibition of marijuana. We can't afford to allow Attorney General Sessions to reinvigorate the failed War on Drugs."

The rider prevents prosecutors from bringing charges against people who legally use medical marijuana in the 29 states that allow it plus Washington, D.C. Among them are New Jersey and Delaware. Pennsylvania plans to make medicinal cannabis available in the coming months. Eight states and Washington, D.C. have legalized marijuana more broadly.

But the rider has limitations, said Sean O'Connor, a University of Washington law professor who leads the school's Cannabis Law and Policy Project. It doesn't protect unauthorized medical marijuana use or adults who use the drug recreationally.

"It gives [Sessions] — and any U.S. attorneys that want to be aggressive — plenty of folks to go after if they want to," O'Connor said.

Much will depend on individual U.S. attorneys, many of whom are still awaiting Senate confirmation. Colorado's U.S. attorney, for example, said his office would not change its approach. The drug is legal there for medical and recreational use.

But in western Pennsylvania, Scott Brady, the top federal prosecutor, told a Pittsburgh TV station that he would "vigorously enforce federal law," and "protect the citizens of western Pennsylvania from those individuals and criminal organizations which traffic in all illegal controlled substances, including marijuana."

Lawmakers hoping to short-circuit such prosecutions could try to legalize marijuana entirely, O'Connor said. "That overrides everything."

Booker introduced a bill to do that last year, arguing that marijuana prosecutions unfairly punish minority communities without improving public safety. The plan hasn't gained much traction, and medical use has more bipartisan support than recreational legalization. Some advocates think Sessions' move could build support for the idea as lawmakers react to a move that might undermine laws in their states and potentially disrupt legal marijuana businesses that have flourished.

"Prosecute Hillary Clinton, not medical marijuana businesses and patients!" tweeted U.S. Rep. Matt Gaetz, a Florida Republican, one of a number of Republicans who reacted harshly to Sessions' announcement.

Sen. Brian Schatz (D., Hawaii), tweeted, "There is a growing bipartisan group of senators that is not going to stand by while Jeff Sessions takes us back several generations on marijuana policy."

The public view on marijuana has softened. A Gallup poll in October found that 64 percent of Americans favor legalization, including 51 percent of Republicans.

But in Congress few specific plans have emerged in the days since Sessions' announcement, and it's unclear if Republicans have the appetite for fully legalizing the drug or counteracting a president who has made law and order central to his agenda.

Another option could be expanding the budget amendment to cover recreational marijuana, and attaching that to a must-pass spending bill to keep the government running, which might leave Trump with little choice but to accept it.

The new Department of Justice guidelines wiped out Obama-era rules that directed federal prosecutors to take a hands-off approach in states that legalized marijuana. The change does not order prosecutions, but opens the door for prosecutors to pursue charges tied to marijuana use if they choose, since the drug remains illegal under federal law.

Lawmakers have several tools they can use to push back and protect state laws and programs. Sen. Cory Gardner (R., Colo.) said he is prepared to block Justice Department nominees until Sessions reverses course. U.S. attorney nominees could also face sharp questions about marijuana prosecutions — and their intended approaches — at confirmation hearings. Lawmakers could try to block nominees if they don't like the answers.

"Devoting our limited resources to prosecuting medical marijuana use that is permitted under Delaware state law is a poor allocation of federal time, money, and manpower that should be focused on more important things, such combating violent crime on our streets," said a statement from Sen. Chris Coons (D., Del.), a member of the Judiciary Committee.

Among the many U.S. attorney nominees still awaiting Senate approval is Bill McSwain, chosen to be the top federal prosecutor in Philadelphia. New Jersey has an interim U.S. attorney, Craig Carpenito, but no one has been nominated yet for a full appointment.

Another less drastic step, O'Connor said, could be to "reschedule" marijuana, moving it off the Drug Enforcement Administration's list of the most dangerous narcotics — like heroin — and regulate it more like a prescription or over-the-counter drug.

Until there is clarity, however, he said the new guidelines could discourage investment in medical marijuana businesses, since banks, insurance companies or delivery drivers may be reluctant to work with such enterprises if they face the possibility of a federal prosecution.

"The real fear is that U.S. attorneys could prosecute anyone who is at all involved," O'Connor said.