WASHINGTON -- Paul Manafort says he's registering with the Justice Department as a foreign agent. Michael Flynn already has. In both cases, the decisions to register by these associates of U.S. President Donald Trump came late -- after the lobbying has already taken place -- and accompanied by an admission that they violated federal law.

The high-profile filings are putting a spotlight on the Foreign Agents Registration Act, a law enacted before World War II with the goal of unmasking foreign influence campaigns in the U.S.

The idea was simple: Lobbyists and others who work on behalf of a foreign government or political interest must disclose to the Justice Department and to the public their work to sway public opinion and U.S. policy.

But the cases of Manafort, who was forced out as Trump's campaign chairman , and Flynn, who was fired as the president's national security adviser , have raised questions, particularly in light of the continuing scrutiny of the foreign entanglements of several Trump associates. A few answers:

Q: WHAT IS THE FOREIGN AGENTS REGISTRATION ACT?

A: Congress enacted the 1938 statute in response to covert Nazi propaganda agents operating in the U.S. It requires individuals who act in the U.S. on behalf of foreign political parties, people or governments to register as foreign agents with the Justice Department.

Registrants are expected to disclose whom they work for and how much they're paid, and to describe their activities. They're also expected to conspicuously disclose that mailings, letters, opinion pieces or other material they distribute are on behalf of a foreign principal, and that additional details about their efforts are available in Justice Department files.

There are exceptions in the law for foreign diplomats and foreign government officials, and for people engaged in solely religious, academic, commercial or scientific activities.

Q: HOW DOES IT WORK?

A: In practice, lobbyists file reports that can list meetings, phone calls and even emails on behalf of their foreign clients. They must disclose the names of people they meet with and the issues they discussed. The foreign agent must register within 10 days of agreeing to perform the foreign work, before beginning any activities. After that, supplemental reports must be filed every six months, as long as the foreign agent work is ongoing, and the Justice Department must be notified when the agreement is terminated.

The reports are posted on a searchable public website: https://www.fara.gov/

Q: WHY DID FLYNN REGISTER?

A: Flynn and his firm, Flynn Intel Group, registered as foreign agents in March for work performed for a Turkish-owned business. In the registration, Flynn acknowledged that the work could have principally benefited Turkey's government. Flynn, a retired U.S. Army lieutenant general and former director of the Defence Intelligence Agency, was on contract with the company while he was a senior Trump campaign adviser. Over the course of the three-month contract with the company, Inovo BV, Flynn's firm was paid $530,000.

Flynn's filing showed the breadth of activities considered foreign-agent work.

While his firm performed some lobbying, most of its work was gathering adverse information on Turkish cleric Fethullah Gulen, who lives in Pennsylvania. Turkish President Recep Tayyip Erdogan blames Gulen for a failed coup attempt in Turkey last summer and is pushing for the U.S. to extradite him. Gulen denies involvement, and the U.S. has rebuffed Erdogan's request.

The goal of Flynn's work, according to his filing, was to develop information that would convince American officials to pursue criminal charges against Gulen. The Associated Press has since learned that Flynn's firm also pushed for a congressional investigation of Gulen during an October meeting. The request was refused.

Q: WHAT PROMPTED MANAFORT TO SAY HE WOULD FILE?

A: His spokesman says Manafort worked to further Ukrainian political interests . Spokesman Jason Maloni confirmed the intent to register months after the AP reported that his consulting firm had orchestrated a covert Washington lobbying operation on behalf of Ukraine's ruling political party. That effort, from 2012 through 2014, was never disclosed to the Justice Department.

Maloni said Manafort began discussions with the U.S. government about his lobbying activities after he joined the Trump campaign. It's unclear whether the conversations came before or after Trump forced Manafort to resign his post, on the same day as the AP report of unregistered lobbying.

The Podesta Group, a Washington lobbying firm, has already retroactively registered for its part in the Ukrainian influence campaign. The firm was one of two that worked under the direction of Manafort and his former deputy, Rick Gates. The other firm involved, Mercury LLC, says it also will register soon.

Q: DOES RETROACTIVE REGISTRATION FLOUT THE LAW?

A: Perhaps, although the Justice Department favours administrative enforcement over criminal punishment and sees value in disclosure no matter when it's made.

"The statute's purpose isn't necessarily served by after-the-fact registration, especially where the registration is after the activity on behalf of a foreign interest has ceased," said Stephen Vladeck, a national security law professor at the University of Texas at Austin.

"But for better or worse, DOJ has at least sometimes allowed individuals to escape liability by registering after the fact, especially in cases in which the initial failure to register appeared to be negligent, not intentional," Vladeck wrote in an email.

In a statement, the Justice Department said it always strives for compliance with the registration requirement and to ensure the accuracy of information about the political activities of those who register.

"This is true whether such information pertains to current or past activity," the statement read. "Requiring registration for past activities ensures that these objectives are met and that an accurate public record is created and maintained."

Q: WHY ARE THESE CASES ONLY RARELY PROSECUTED?

A: Transparency, rather than punishment, is the law's primary purpose. "Not every violation is worth prosecuting," said Amy Jeffress, a former Justice Department national security official. Federal prosecutors typically don't prosecute failure to disclose unless they can prove that it was intentional, she said.

Dan Pickard, a partner at the Washington law firm Wiley Rein, said that proving criminal intent can be difficult because of the obscurity of the foreign agent law. "To show a wilful intent not to register is a tall order," Pickard said.

An August report from the department's inspector general's office counted seven criminal cases under the law between 1966 and 2015, and cited "differing understandings" between FBI officials and Justice Department prosecutors about the statute's intent. Justice Department officials believe the law's primary purpose is not to secure criminal convictions. They cite a separate statute, which makes it a crime to spy or conduct other espionage-like activities on behalf of a foreign government, as a point of focus. But FBI officials say they believe federal prosecutors aren't aggressive enough in pursuing punishments for people who fail to register.

Q: HOW DOES THE JUSTICE DEPARTMENT ENFORCE THE LAW?

A: A small staff in the Foreign Agent Registration Act unit keeps the records and undertakes open-source research.

The unit routinely combs the Lobbying Disclosure Act database and news reports looking for lobbying work that should be disclosed as foreign agent work. When the unit finds a likely case, it sends letters of inquiry to the lobbying firms, asking them to turn over documentation and to register as foreign agents if the work qualifies.

There's a catch, though. The letters don't have the same power as a subpoena, meaning the unit relies on voluntary disclosure. The Justice Department has pushed for Congress to grant subpoena authority in cases going back to the early 1990s. So far, Congress hasn't given it.