In this occasional series, we will bring you up to speed on the biggest national security stories of the week.

Investigators are scrutinizing a series of meetings held by President Trump’s son-in-law and White House adviser Jared Kushner as part of their investigation into Russian interference in the 2016 presidential election, according to people familiar with the investigation. Kushner joined the administration in early January to focus on Middle East policy and trade. He recently traveled with Trump on the president’s first trip abroad.

Here’s what you need to know about Kushner and the Russia investigation:

What are investigators looking into?
Law enforcement officials are examining Kushner’s meetings in December with a Russian banker and the Russian ambassador. Both encounters have already been reported, but investigators are focused on the extent and nature of those meetings.

Kushner — along with former national security adviser Michael Flynn — met with Russian ambassador Sergey Kislyak for about 20 minutes at Trump Tower in New York. The White House confirmed the meeting, saying “it made sense to establish a line of communication.” Later that month, Flynn called the Russian ambassador to discuss the sanctions — a phone call that he lied about to Vice President Pence and that eventually led him to resign.

Kislyak requested a follow-up meeting with Kushner in December, but Kushner sent an aide in his place.

Kushner also met in December with Russian banker Sergey Gorkov, the head of Vnesheconombank, a meeting that lasted for about 30 minutes. The bank was placed on the U.S. sanctions list after Russia annexed Crimea in 2014.

Why is this significant?
Along with Flynn, the investigation into Russia’s interference has also embroiled Attorney General Jeff Sessions and former campaign chairman Paul Manafort. But Kushner is the only White House official now connected to the investigation. He’s also the closest to Trump and has been described as his confidant. During the campaign, Trump relied heavily on Kushner’s advice.

Kushner also omitted mentioning his December contacts with the Russians when applying for top security clearance. The application requires an individual to disclose all recent contacts with foreign nationals. Kushner’s lawyer called it an error and said the forms would be revised.

This week, CNN also reported that Sessions omitted his contacts with Russian officials from a security clearance form when he was preparing to serve as the attorney general. This was the same information Sessions left out during his confirmation hearing, which eventually led him to recuse himself from the Russia investigation. Sessions met with Kislyak twice before Trump stepped into office.

What does this mean for Kushner?
To be clear, Kushner has not been accused of any wrongdoing. Also, The Washington Post has not been told that Kushner is a “target” of the investigation, a word that generally refers to someone who is the main suspect. However, prosecutors can and do bring charges against individuals who are not designated as targets.

Jamie Gorelick, one of Kushner’s attorneys, said Kushner is willing to share what he knows.

“Mr. Kushner previously volunteered to share with Congress what he knows about these meetings. He will do the same if he is contacted in connection with any other inquiry,” Gorelick said.

Who else wants to know more about Kushner’s Russia ties?
The Senate Intelligence Committee, which is also conducting its own review into possible Russian meddling. Kushner agreed in March to testify in front of lawmakers, who are gathering a list of witnesses and scheduling interviews.

“We expect him to be able to provide answers to key questions that have arisen in our inquiry,” said Committee Chairman Richard Burr (R-N.C.) and Mark R. Warner (D-Va.) in a joint statement.

The timing of the testimony has yet to be determined.

Meanwhile, the investigation has significantly expanded, with former FBI Director Robert S. Mueller III  overseeing the probe as special counsel. Investigators are now “issuing subpoenas and looking to conduct interviews,” The Post reports, and certain lawmakers have been notified about the change of pace.

Read previous briefs:

What’s next in the Russia investigation? The week’s biggest bombshells.