Washington • In his last year in office, President Barack Obama signed a bill that stripped the Drug Enforcement Administration of its most powerful tool for combating drug companies suspected of spilling prescription pain pills outside the legal distribution chain.

But did the president know the import of what he was signing?

In the spring of 2016, a handful of members of Congress, allied with the nation's major drug distributors, prevailed upon the DEA and the Justice Department to agree to a more industry-friendly law, undermining efforts to stanch the flow of pain pills, according to an investigation by The Washington Post and "60 Minutes." The DEA had opposed the effort for years.

The Ensuring Patient Access and Effective Drug Enforcement Act was the crowning achievement of a multifaceted campaign by the drug industry to weaken aggressive DEA enforcement efforts against drug distribution companies that were supplying corrupt doctors and pharmacists who peddled narcotics to the black market. The industry worked behind the scenes with lobbyists and key members of Congress, pouring more than a million dollars into their election campaigns.

The chief advocate of the law that hobbled the DEA was Rep. Tom Marino, a Pennsylvania Republican who is now President Donald Trump's nominee to become the nation's next drug czar. Marino spent years trying to move the law through Congress. It passed after Sen. Orrin Hatch, R-Utah , negotiated a final version with the DEA.

Besides the sponsors and co-sponsors of the bill, few lawmakers knew the true impact the law would have. It sailed through Congress without debate and was passed by unanimous consent, a parliamentary procedure reserved for bills considered to be noncontroversial. The White House was equally unaware of the bill's import when Obama signed it into law, according to interviews with former senior administration officials.

Top officials at the White House and the Justice Department have declined to discuss how the bill came to pass.

Michael Botticelli, who led the White House Office of National Drug Control Policy at the time, said neither Justice nor the DEA objected to the bill, removing a major obstacle to the president's approval.

"We deferred to DEA, as is common practice," he said.

The bill also was reviewed by the White House Office of Management and Budget.

"Neither the DEA nor the Justice Department informed OMB about the policy change in the bill," a former senior OMB official with knowledge of the issue said recently. The official spoke on the condition of anonymity because of the sensitivity of internal White House deliberations.

The DEA's top official at the time, acting administrator Chuck Rosenberg, declined repeated requests for interviews. A senior DEA official said the agency fought the bill for years in the face of growing pressure from key members of Congress and industry lobbyists. But the DEA lost the battle and eventually was forced to accept a deal it did not want.

"They would have passed this with us or without us," said the official, who spoke on the condition of anonymity. "Our point was that this law was completely unnecessary."

Loretta E. Lynch, who was attorney general at the time, declined a recent interview request.

Obama also declined to discuss the law. His spokeswoman, Katie Hill, referred reporters to Botticelli's statement.

The DEA and Justice Department have denied or delayed more than a dozen requests filed by The Post and "60 Minutes" under the Freedom of Information Act for public records that might shed additional light on the matter. Some of those requests have been pending for nearly 18 months. The Post is now suing the Justice Department in federal court for some of those records.

Hatch's spokesman, Matt Whitlock, said the DEA, which had undergone a leadership change, did not oppose the bill in the end.

"We worked collaboratively with DEA and DOJ . . . and they contributed significantly to the language of the bill," Whitlock wrote in an email. "DEA had plenty of opportunities to stop the bill and they did not do so."

Marino declined repeated requests for comment. Marino's staff called the Capitol Police when The Post and "60 Minutes" tried to interview the congressman at his office on Sept. 12. In the past, the congressman has said the DEA was too aggressive and needed to work more collaboratively with drug companies.

The law gained momentum in 2015, when the Justice Department named a new DEA chief — Rosenberg — who said he wanted to mend the rift between the agency and the drug industry.

"Rosenberg wanted to paint a new face on the DEA for the Hill," said Regina LaBelle, the chief of staff for the White House's Officer of National Drug Control Policy at the time. "He wanted to show them the softer side of the DEA, and he wanted to work with industry."

In October 2015, one of the last remaining obstacles to the bill was removed. Joseph T. Rannazzisi, the DEA's longtime chief of diversion control and an adamant opponent of the Marino bill, retired after a 30-year career.

Pressure from Congress, which had generated a Justice Deparment inspector general's investigation, helped to drive him out. The investigation went nowhere, but Rannazzisi said, "It destroyed me."

By then the DEA was in negotiations with Hatch's staff to amend the bill for the Senate's consideration.

The newly proposed language required the DEA to show that a company's conduct posed a "substantial likelihood of an immediate threat" of death, serious bodily harm or drug abuse before the agency could seek a suspension order.

DEA and Justice officials had said in emails and memos that the higher standard posed a nearly impossible bar for the agency to clear for cases against distributors and manufacturers because they are so far away from the street.

Whitlock, Hatch's spokesman, said the new language was proposed by the DEA.

You bet we have a response to the Washington Post opioid story today -- https://t.co/4csPS02EPy #utpol — Matt Whitlock 🇺🇸 (@mattdizwhitlock) October 16, 2017

The biggest question everyone should be asking is if they had these concerns then why did they A) allow it to pass by unanimous consent, — Matt Whitlock 🇺🇸 (@mattdizwhitlock) October 16, 2017

a procedure reserved for noncontroversial bills where there is stakeholder consensus, and B) why didn't they urge their boss (POTUS) to veto — Matt Whitlock 🇺🇸 (@mattdizwhitlock) October 16, 2017

DEA/ DOJ had a number of tools at their disposal to stop this bill from becoming law. They didn't use any of them. https://t.co/4csPS02EPy — Matt Whitlock 🇺🇸 (@mattdizwhitlock) October 16, 2017

We can only guess that they didn't because like us, they believed the bill would increase collaboration and help fight the opioid crisis. — Matt Whitlock 🇺🇸 (@mattdizwhitlock) October 16, 2017

"Senator Hatch has had a strong working relationship with DEA for his entire term of service and worked collaboratively for months with DEA here. Any claim that he tried to steamroll DEA or would ever seek to steamroll DEA is simply incorrect."

A Nov. 30 email from Jill Wade Tyson, a Justice Department congressional liaison officer, to a Senate staffer shows that the DEA agreed to the bill with reluctance.

"DEA felt this wasn't a great solution, but was the best of the options offered to us, even if it did not fully address the concerns we had previously laid out for you," she added, according to the email, which was provided by staff of Sen. Sheldon Whitehouse (D-R.I.), one of the bill's co-sponsors.

On March 17, 2016, the Senate passed the bill by unanimous consent. On April 12, the House approved the Senate version, also by unanimous consent.