WASHINGTON — Justice Department officials have seized the phones of two top advisers to former President Donald Trump and blanketed his aides with about 40 subpoenas in a substantial escalation of the investigation into his efforts to subvert the 2020 election, people familiar with the inquiry said Monday.

The seizure of the phones, coupled with a widening effort to obtain information from those around Trump after the 2020 election, represent some of the most aggressive steps the department has taken thus far in its criminal investigation into the actions that led to the Jan. 6, 2021, assault on the Capitol by a pro-Trump mob.

The extent of the investigation has come into focus in recent days, even though it has often been overshadowed by the government's legal clash with Trump and his lawyers over a separate inquiry into the handling of presidential records, including highly classified materials, the former president kept at Mar-a-Lago, his residence in Florida.

Federal agents with court-authorized search warrants took phones last week from at least two people: Boris Epshteyn, an in-house counsel who helps coordinate Trump's legal efforts, and Mike Roman, a campaign strategist who was the director of Election Day operations for the Trump campaign in 2020, people familiar with the investigation said.

Epshteyn and Roman have been linked to a critical element of Trump's bid to hold onto power: the effort to name slates of electors pledged to Trump from swing states won by Joe Biden in 2020 as part of a plan to block or delay congressional certification of Biden's Electoral College victory.

Epshteyn and Roman did not respond to requests for comment. A Justice Department spokesperson declined to comment.

The names of those receiving the latest round of subpoenas in the investigation related to Jan. 6 have dribbled out gradually, with investigators casting a wide net on a range of issues, including Trump's postelection fundraising and the so-called fake electors scheme.

One of the recipients, people familiar with the case said, was Dan Scavino, Trump's former social media director who rose from working at a Trump-owned golf course to become one of his most loyal West Wing aides, and has remained an adviser since Trump left office. Stanley Woodward, one of Scavino's lawyers, declined to comment.

Another was Bernard B. Kerik, a former New York City police commissioner. Kerik, who promoted claims of voter fraud alongside his friend Rudy Giuliani, was issued a subpoena by prosecutors with the U.S. attorney's office in Washington, his lawyer, Timothy Parlatore, said Monday. Parlatore said his client had initially offered to grant an interview voluntarily.

The subpoenas seek information in connection with the fake electors plan.

For months, associates of Trump's have received subpoenas related to other aspects of the investigations into his efforts to cling to power. But in a new line of inquiry, some of the latest subpoenas focus on the activities of the Save America political action committee, the main political fundraising conduit for Trump since he left office.

The fact that the Justice Department is now seeking information related to fundraising comes as the House committee examining the Jan. 6 attack has raised questions about money Trump solicited under the premise of fighting election fraud.

The new subpoenas encompass a wide variety of those in Trump's orbit, from low-level aides to his most senior advisers.

The Justice Department has spent more than a year focused on investigating hundreds of rioters who were on the ground at the Capitol on Jan. 6. But this past spring, it started issuing grand jury subpoenas to people such as Ali Alexander, a prominent organizer with the pro-Trump Stop the Steal group, who helped plan the march to the Capitol after Trump gave a speech that day at the Ellipse near the White House.

Although it remains unclear how many subpoenas had been issued in that early round, the information they sought was broad.

According to a subpoena obtained by The New York Times, they asked for any records or communications from people who organized, spoke at or provided security for Trump's rally at the Ellipse. They also requested information about any members of the executive and legislative branches who may have taken part in planning or executing the rally, or tried to "obstruct, influence, impede or delay" the certification of the presidential election.

By early summer, the grand jury investigation had taken another turn as several subpoenas were issued to state lawmakers and state Republican officials allied with Trump who took part in a plan to create fake slates of pro-Trump electors in several key swing states actually won by Biden.

At least 20 of these subpoenas were sent out and sought information about, and communications with, several lawyers who took part in the fake elector scheme, including Giuliani and John Eastman.

About the same time, federal investigators seized Eastman's cellphone and the phone of another lawyer, Jeffrey Clark, whom Trump had sought at one point to install as the acting attorney general. Clark had his own role in the fake elector scheme: In December 2020, he helped draft a letter to Georgia Gov. Brian Kemp, saying that the state's election results had been marred by fraud and recommending that Kemp convene a special session of the Georgia legislature to create a slate of pro-Trump electors.

At least some of the new subpoenas also requested all records that the recipients had turned over to the House Jan. 6 committee, according to a person familiar with the matter.