A target letter sent to Donald Trump suggests that a sprawling Justice Department investigation into efforts to overturn the 2020 election is zeroing in on him after more than a year of interviews with top aides to the former president and state officials from across the country.

Federal prosecutors have cast a wide net, asking witnesses in recent months about a chaotic White House meeting that included discussion of seizing voting machines and about lawyers' involvement in plans to block the transfer of power, according to people familiar with the probe. They've discussed with witnesses schemes by Trump associates to enlist slates of Republican fake electors in battleground states won by Democrat Joe Biden and interviewed state election officials who faced a pressure campaign over the election results in the days before the Jan. 6 riot at the U.S. Capitol.

It is unclear how much longer special counsel Jack Smith's investigation will last, but its gravity was evident Tuesday when Trump disclosed that he had received a letter from the Justice Department advising him that he was a target of the probe. Such letters often precede criminal charges; Trump received one ahead of his indictment last month on charges that he illegally hoarded classified documents at his Mar-a-Lago property in Florida.

Though it's not known what charges Trump or anyone else might face in the election probe, the scope of the inquiry stands in stark contrast to Smith's much narrower classified documents investigation. The vast range of witnesses is a reminder of the tumultuous two months between Trump's election loss and the insurrection at the Capitol, when some lawyers and advisers aided his futile efforts to remain president while many others implored him to move on or were relentlessly badgered to help alter results.

Trump joked about his legal challenges while campaigning in eastern Iowa on Tuesday night, just hours after announcing he’d received the target letter.

Headlining a Republican county meeting, Trump attacked investigators while trying to make light of what could be his third criminal indictment since March.

“I didn’t know practically what a subpoena was and grand juries. Now I’m becoming an expert,” he told the audience at an Elks Lodge in Cedar Rapids.

Trump also taped an interview with Fox News host Sean Hannity in front of a live audience, where he vented his frustrations. “It bothers me,” he said as he continued to cast the cases as politically motivated. “It’s a disgrace what’s happening to our country.”

A spokesperson for Smith declined to comment about the target letter or the interviews that prosecutors have conducted.

Even before Smith inherited the election interference probe last November, Justice Department investigators had already interviewed multiple Trump administration officials, including the chief of staff to former Vice President Mike Pence and former top lawyers at the White House, scrutinized post-election fundraising and seized as potential evidence the cellphones of numerous lawyers and officials.

Since then, Smith's team has questioned senior administration officials including Pence himself before the grand jury in Washington and has conducted voluntary interviews with a wide array of witnesses inside and outside the federal government. Those include election officials in states where Trump associates waged fruitless efforts to get results overturned in the Republican incumbent's favor.

Georgia Secretary of State Brad Raffensperger, who was personally lobbied by Trump to "find 11,780 votes" to overtake Biden, has been interviewed by Smith's team, as has Michigan Secretary of State Jocelyn Benson and New Mexico Secretary of State Maggie Toulouse Oliver, according to their representatives.

Wisconsin's top elections administrator and election leaders in Milwaukee and Madison have spoken with federal investigators. And former Arizona Republican Gov. Doug Ducey, who silenced a call from the Trump White House as he was publicly certifying Biden's narrow victory in the state, has been contacted by Smith's team, a spokesperson said Tuesday.

A consistent area of interest for investigators has been the role played by Trump lawyers in helping him cling to power, according to people familiar with the investigation who, like others interviewed for the story, spoke on condition of anonymity to discuss an ongoing criminal probe.

John Eastman, a conservative law professor, advanced a dubious legal theory that said Pence could halt the certification of state electoral votes to block Biden's win. Another lawyer, Sidney Powell, promoted baseless claims of voter fraud and pushed an idea — vigorously opposed by Trump's lawyers at the White House — that Trump had the authority under an earlier executive order to seize state voting machines.

Charles Burnham, a lawyer for Eastman, said Tuesday that his client had not received a target letter. "We don't expect one since raising concerns about illegality in the conduct of an election is not now and has never been sanctionable," he said. A lawyer for Powell declined to comment.

Multiple witnesses have been asked about a heated Dec. 18, 2020, meeting at the White House in which outside advisers, including Powell, raised the voting machines idea, people familiar with the matter said. The meeting, which devolved into a shouting match, featured prominently in a separate investigation by the House Jan. 6 committee, with former White House official Cassidy Hutchinson memorably describing it as "unhinged."

Rudy Giuliani, a Trump lawyer who participated in the meeting and who spearheaded legal challenges to the election results, was asked about that meeting during a voluntary interview with Smith's team and also detailed to prosecutors Powell's involvement in failed efforts to overturn the election, according to a person familiar with his account. Giuliani has not received a target letter.

Giuliani's interview was part of what's known as a proffer agreement, the person said, in which a person agrees to speak voluntarily with investigators while prosecutors agree not to use those statements in any criminal case they might later bring. Prosecutors have worked to negotiate similar arrangements with other witnesses.

As prosecutors dig into efforts by Trump allies to thwart Biden's victory, they've focused on the creation of slates of fake electors from key states captured by Biden who were enlisted by Trump and his allies to sign false certificates stating that Trump had actually won.

Smith's team has also focused on Trump's efforts to punish officials from his administration who refused to go along with his false election fraud claims. Chris Krebs, who was fired by Trump as director of the Department of Homeland Security's cybersecurity agency after vouching for the integrity of the 2020 vote, was interviewed by prosecutors a couple of months ago about the perceived retaliation for his stance, according to a person familiar with the questioning.

Another person familiar with Smith's investigation also said prosecutors in recent months have expressed interest in the ordeal of Ruby Freeman, a Georgia election worker who along with her daughter recounted to the House Jan. 6 committee how their lives became upended when Trump and allies latched onto surveillance footage to level since-debunked allegations of voter fraud.