But through subpoenas and search warrants, the department has made clear that it is pursuing at least two related lines of inquiry that could lead to Mr. Trump.

One centers on the so-called fake electors. In that line of inquiry, prosecutors have issued subpoenas to some people who had signed up to be on the list of those purporting to be electors that pro-Trump forces wanted to use to help block certification of the Electoral College results by Congress on Jan. 6, 2021.

Investigation of the fake electors scheme has fallen under Thomas Windom, a prosecutor brought in by the Justice Department last year to help bolster its efforts. Mr. Windom’s team has also issued subpoenas to a wide range of characters connected to the Jan. 6 attacks, seeking information about lawyers who worked closely with Mr. Trump, including Mr. Giuliani and John Eastman, the little-known conservative lawyer who tried to help Mr. Trump find a way to block congressional certification of the election results…

The other line of Justice Department inquiry centers on the effort by a Trump-era Justice Department official, Jeffrey Clark, to pressure Georgia officials not to certify the state’s election results by sending a letter falsely suggesting that the department had found evidence of election fraud there.