What you need to know about Susan Rice and the unmasking controversy

— -- Unmasking is the word of the week in Washington, D.C.

What's in question is whether former national security adviser Susan Rice did anything wrong by unmasking names in a classified foreign intelligence report that turned out to include campaign and transition associates of President Donald Trump.

Allies of Trump are suggesting that her actions prove the president's unsubstantiated claims from a month ago that he was wiretapped at Trump Tower by the Obama administration.

Trump himself said Wednesday that he believes Rice may have committed a crime. “I think it’s going to be the biggest story,” Trump told The New York Times. “It’s such an important story for our country and the world. It is one of the big stories of our time.” The president did not offer any evidence for his claims.

But Rice staunchly denies any allegations of wrongdoing. On Tuesday, she told MSNBC that it's "absolutely false" that she or any other Obama administration officials unmasked names of Trump's presidential campaign and transition team members for political purposes. "I leaked nothing to nobody," she said. On Wednesday, she said of Trump's comments, "I'm not going to dignify the president's ludicrous charge with a comment."

Nevertheless, Rice, who has a history of being a controversial figure within the Obama administration, was involved in examining intelligence related to individuals affiliated with Trump's campaign and transition team, and her actions are being heavily scrutinized.

Here's what we know:

What is unmasking?

Unmasking is a term used by the intelligence community to describe the process of unveiling the identity of a U.S. person who appears in a classified foreign intelligence report. The law requires that identities of U.S. persons picked up or mentioned during the course of foreign surveillance be masked; that is, that they be shielded from people reading the reports.

However, there are 20 high-ranking officials within the U.S. government who have to power to approve requests to reveal those identities if they deem that information is necessary to understanding the value of the intelligence. That process is called "unmasking," and Rice had the authority to do so while serving as national security adviser.

When a name is unmasked it is only provided to the official who requested it, and therefore unmasking is not equivalent to leaking the name.

Trump's original claims

Much of this story goes back to a series of Saturday morning tweets from President Trump on March 4, when he said that the Obama White House wiretapped him at Trump Tower during the campaign. FBI Director James Comey and the director of the National Security Agency, Mike Rogers, have since said they have seen no evidence to back up Trump's allegations.

A source close to the matter told ABC News that Trump had no knowledge of the unmasking when he wrote those tweets.

The White House never explained exactly why Trump tweeted what he did, but right-leaning news reports making that claim were brought to Trump's attention at the time, as previously reported by ABC News.

What did Rice do?

Rice acknowledged Tuesday that she engaged in unmasking Trump officials late in President Barack Obama's term, but insisted it was not politically motivated as her detractors have suggested. She called the unmasking process routine and said she only did it when it pertained to matters of national security.

Rice did not detail which Trump officials she unmasked or why, but current and former U.S. officials have told ABC News it happened on a number of occasions. In many instances, one official said, she did it to understand, per Obama's request, how far Russian meddling in the presidential election had gone and whether or not there was any possible collusion with Trump officials.

Rice alluded to that Russia probe in her interview, saying it was of "grave concern." Ultimately, she said no evidence of collusion between Russian officials and Trump associates was found, and that finding was shared by the intelligence community in a report at the end of Obama's term.

However, the probe into Russia's interference in the election is ongoing and the subject of two congressional investigations.

A source also told ABC News that on one occasion Rice requested the unmasking of Trump transition officials in a foreign intelligence report that had nothing to do with Russia.

Rice is also under fire for comments she made last month in an interview with "PBS NewsHour" in which she said "I know nothing about this," when asked about claims from Rep. Devin Nunes, R-California, that Trump officials were caught up in surveillance and that their identities were disclosed. Rice later clarified she was saying she didn't know what reports Nunes was referring to and said "I still do not."

Nunes' controversial announcement

Rep. Devin Nunes, the chairman of the House Intelligence Committee, caused a firestorm last month when he held a press conference in which he indicated that members of the Trump transition team, and possibly the president, were incidentally surveilled in a way that could be improper.

The press conference came after Nunes reviewed classified documents that he says he got from a secret source. Nunes has provided limited details about the information he obtained, but said there are "dozens of reports" showing that "incidentally collected information about U.S. citizens involved in the Trump transition" was gathered during the course of "normal foreign surveillance."

Nunes first viewed the documents on White House grounds a day before briefing the president, creating an air of suspicion that he was doing the White House's bidding. Nunes has denied acting on behalf of the White House.

It was Nunes who first raised the unmasking allegations, saying that some names were unmasked in the documents he reviewed. Nunes later clarified that "for the most part" the names were not revealed, but "it was pretty clear who they were talking about," he told CNN in late March. Nunes has since said he was unsure whether associates of Trump participated in the intercepted communications or whether those persons were simply mentioned or referred to by others.

Nunes was heavily criticized for making the announcement to the press and briefing the White House before he shared the information with the rest of the intelligence committee. Weeks after that press conference, only Nunes' Democratic counterpart, Rep. Adam Schiff, D-California, has seen those documents and they have still not been shared with the full committee.

Nunes has apologized for the way he presented his information, but that hasn't stopped Democratic and Republican leaders alike from questioning his ability to oversee a fair investigation of the Russia matter. Nunes has said he will not step down from his position as chair of the House Intelligence Committee.

ABC News' Adam Kelsey contributed to this report.