The Department of Justice's internal watchdog will investigate the Trump-era seizure of communication records from some Democratic lawmakers and journalists, the agency announced Friday.

It joins a burgeoning effort in Congress to unearth more details about what happened in 2017 when the DOJ under President Donald Trump asked Apple to turn over communication metadata for at least two Democratic House members, their staff and family members. The investigation became public on Thursday in a report by The New York Times.

Separately on Friday, Democrats Senate Majority Leader Chuck Schumer and Judiciary Committee Chairman Dick Durbin threatened to subpoena former attorneys general William Barr and Jeff Sessions to testify before Congress about the investigations.

Democrats on the House Intelligence have grown frustrated since learning last month their data was targeted and have been unable to get more information from the Department of Justice, according to a House official.

A House Intelligence Committee official said Friday that the panel's Chairman Rep. Adam Schiff, who was among those targeted, has been unable to obtain information about the subpoena from Biden administration officials. For instance, the committee specifically asked what metadata was included in the subpoenas and the Justice Department has not provided answers, the official said.

“We have repeatedly posed basic and readily answerable questions to the Department for more than a month, but have received virtually no information beyond a confirmation that the investigation is closed,” the aide said in a statement. “The Department's refusal to provide information is unacceptable, and they will need to provide a full accounting of this and other instances in which law enforcement was weaponized against Donald Trump's political opponents.”

The official added that the only notification of the subpoenas came via email from Apple — an email that some who saw it believed might be spam, until they checked further.

The New York Times reported Thursday that under former President Donald Trump, the Justice Department subpoenaed metadata in February 2018 from Apple related to accounts belonging to at least two Democrats on the House Intelligence Committee. Their aides and family members, including a minor, were targeted as well. A source confirmed to NBC News that the lawmakers and staff had been notified by Apple.

The New York Times, CNN and The Washington Post previously disclosed they were notified recently by the DOJ that records of reporters at their outlets were obtained.

Rep. Eric Swalwell, D-Calif., a frequent and vocal critic of Trump, was also targeted.

At the time the records were sought, the House Intelligence Committee was investigating Russian interference in the 2016 election. The newspaper reported that the records were sought as part of an investigation into leaks of classified information.

Mary McCord, a Georgetown law professor who was the acting head of the DOJ's National Security Division until May 2017, said Sessions was "very interested in pursuing leak investigations" early in the Trump administration.

"Under department practice, any investigation into an elected official would have been considered a sensitive matter that would have required high-level approval," she said.

Schumer and Durbin said in a statement that Congress and the Justice Department’s inspector general must investigate these actions by the Trump administration.

“Former Attorneys General Barr and Sessions and other officials who were involved must testify before the Senate Judiciary Committee under oath. If they refuse, they are subject to being subpoenaed and compelled to testify under oath,” their statement said.

Schumer and Durbin said that the Justice Department must also provide information to the Judiciary Committee about what they called an “gross abuse of power” and “an assault on the separation of powers.”

Courtesy NBC News

And of course it comes back to Russia.

Senator Burr (R) - "The Trump administration actively encouraged and participated in Russian efforts to affect the 2016 election."