Rep. Tom Marino (R-Pa.) was a major supporter of legislation that weakened the Drug Enforcement Administration’s ability to crack down on drug distributors. (Bill Clark/CQ Roll Call)

President Trump announced Tuesday that Rep. Tom Marino (R-Pa.), his nominee for drug czar, was withdrawing in the wake of an investigative report detailing how he helped pass legislation weakening the Drug Enforcement Administration’s ability to go after drug distributors, even as opioid-related deaths continue to rise.

With Marino’s withdrawal — announced by the president in a morning tweet — the administration’s scrutiny of the law intensified. Deputy Attorney General Rod J. Rosenstein said he was “very concerned about it” and planned to review whether the DEA needs “more tools” to carry out its mission.

But it was unclear how aggressively Congress will reassess a bill that was passed last year with no opposition. A spokesman for Sen. Charles E. Grassley (R-Iowa), chairman of the Senate Judiciary Committee, said the panel was exploring “the idea of holding an oversight hearing” to learn what had changed since President Barack Obama signed the bill.

Democratic lawmakers, meanwhile, sought to increase pressure for action and cheered Marino’s exit. They argued that his nomination demonstrated a lack of commitment from Trump to addressing the opioid crisis that has gripped the nation.

A Washington Post/“60 Minutes” investigation published Sunday explained how a targeted lobbying effort helped bolster legislation, known as the Ensuring Patient Access and Effective Drug Enforcement Act, that made it harder for the DEA to act against giant drug distributors, some of which were fined for repeatedly ignoring warnings from the agency to shut down suspicious sales of hundreds of millions of pills.

The law makes it virtually impossible for the DEA to freeze such questionable shipments from the companies, according to internal agency and Justice Department documents and an independent assessment by the agency’s chief administrative law judge in a soon-to-be-published law review article. That powerful tool had allowed the DEA to immediately prevent narcotic painkillers from spilling into the black market.

“As a former prosecutor who has dedicated my life to aggressive and faithful enforcement of our laws, I have reached the difficult decision that the best course of action is to remove the distraction my nomination has created to the utterly vital mission of this premier agency,” Marino said in a statement Tuesday.

But he defended his legislation, saying it was “a balanced solution for ensuring those who genuinely needed access to certain medications were able to do.”

Rep. Judy Chu (D-Calif.), an original co-sponsor of the bill, called Tuesday for an investigation into whether the law is harming enforcement and for hearings to examine whether she was misled about its impact.

Chu, one of only a few Democrats to put her name on the bill, said then-acting DEA administrator Chuck Rosenberg — who has declined repeated interview requests — told her in a meeting last year after the measure became law that it “did not interfere with the DEA’s ability to successfully stop bad actors.”

A letter sent by Chu on Tuesday to two House committee chairmen is the first account of Rosenberg’s position on the law.

Chu said in her letter that she had thought the law “would help independent and community pharmacists, most of whom are small business owners who provide vital services for their communities.”

In another development Tuesday, the nation’s largest drug manufacturing lobby broke ranks with the distributors and urged the law’s repeal.

“We need to ensure the Drug Enforcement Administration (DEA) has sufficient controls and authorities in place to prevent illicit diversion of controlled substances,” Stephen J. Ubl, president and CEO of the Pharmaceutical Research and Manufacturers of America, said in a statement.

He also said Congress should consider whether existing criminal and civil penalties are sufficient to ensure reporting of suspicious orders of controlled substances in a timely fashion.

Trump declined Monday to express support for Marino, nominated in September to lead the Office of National Drug Control Policy, when asked about him during a news conference.

On Tuesday, the president took to Twitter to inform the nation of Marino’s withdrawal, while adding: “Tom is a fine man and a great Congressman!”

Trump has pledged to declare a national emergency next week to address the opioid crisis — a move he first promised in August, when he said the epidemic exceeded anything he had seen involving drugs in his lifetime.

Marino, 65, represents Pennsylvania’s 10th Congressional District, a solid-red, mostly rural area that voted overwhelmingly for Trump last year.

In his statement, Marino said he looks forward “to remaining in service to the people of Pennsylvania’s Tenth Congressional District and continuing my long record of championing solutions to better equip law enforcement to combat drugs.”

Marino’s staff called the Capitol Police when The Post and “60 Minutes” tried to interview the congressman at his office last month. In the past, Marino has said the DEA was too aggressive and needed to work more collaboratively with drug companies.

After reports of Marino’s withdrawal Tuesday, Senate Minority Leader Charles E. Schumer (D-N.Y.) called Trump’s announcement “the right decision” but said the nomination “is further evidence that when it comes to the opioid crisis, the Trump administration talks the talk, but refuses to walk the walk.”

Sen. Joe Manchin III (D-W.Va.), whose state has been hard hit by the opioid epidemic, and who was among the first to call for Marino’s nomination to be withdrawn, said he welcomed the news.

“We need a drug czar who has seen these devastating effects and who is passionate about ending this opioid epidemic,” Manchin said in a statement. “I look forward to working with President Trump to find a drug czar that will serve West Virginians and our entire country.”

Sen. Claire McCaskill (D-Mo.), who plans to introduce a measure that would repeal the law weakening the DEA’s authority, said Tuesday that she is trying to find a larger piece of legislation that could serve as a vehicle for the repeal effort.

“There certainly will be a vehicle by the end of the year,” McCaskill said. “We’re going to have several must-pass things at the end of the year, if we can’t do it before.”

A senior aide to Schumer said that Democratic leaders were “still determining the best possible path” for a repeal effort.

Several Republicans who worked on the legislation have pushed back against critics of the law, arguing that it was vetted with the proper agencies and there was plenty of time for any objections to be heard.

“The Obama administration’s Justice Department and the DEA both were consulted on and approved of the Ensuring Patient Access and Effective Drug Enforcement Act before it was unanimously approved by Congress and signed into law by President Obama,” the Grassley spokesman said.

He added, “The committee is exploring the idea of holding an oversight hearing to determine whether the agencies’ positions have changed and whether changes are needed to the law.”

Marino spent years trying to move such legislation through Congress.

The Post and “60 Minutes” reported Sunday that DEA and Justice Department representatives signed off on the final wording of the bill that became law after lengthy negotiations with the staff of Sen. Orrin G. Hatch (R-Utah) — a point Hatch made in a speech on the Senate floor Monday.

But the DEA officials said the agency was forced to accept a compromise it did not want to avoid language that would have crippled enforcement even more. Emails cited in the report supported that position.

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

The DEA’s chief administrative law judge, John J. Mulrooney II, has concluded that the law makes it all but impossible for the agency to freeze the shipments of large drug distributors via an “immediate suspension order.”

“If it had been the intent of Congress to completely eliminate the DEA’s ability to ever impose an immediate suspension on distributors or manufacturers, it would be difficult to conceive of a more effective vehicle for achieving that goal,” Mulrooney wrote in an article to be published in the Marquette Law Review.

The DEA did not respond to requests for comment Tuesday. Top Obama administration officials have declined to discuss how the bill came to pass.

Anne Gearan, Karoun Demirjian, Sari Horwitz and Ed O’Keefe contributed to this report.