What is a target letter? What to know about the document Trump received from DOJ special counsel Jack Smith

Former President Donald Trump said Tuesday he received a letter Sunday informing him that he is a target of Justice Department special counsel Jack Smith's investigation into efforts to interfere with the peaceful transfer of power following the 2020 election.

A target letter is official correspondence that prosecutors send to people under investigation, CBS News legal contributor and Loyola Law School professor Jessica Levinson explained. It alerts the recipient that they are under investigation, and that the investigation is nearing the final stages.

"And usually, as this target letter apparently did, to say to the person 'you can come and testify before the grand jury," Levinson said.