Jan. 6 charges against Trump would likely include one that hasn't been used since the Civil War

Donald Trump revealed that he was sent a target letter by special counsel Jack Smith as part of the Jan. 6 investigation, and if he's indicted the charges will be serious.

It's not exactly clear what charges Trump would face, but legal experts have concluded the former president would likely face indictment on charges that date back to the Civil War in connection with his role in the insurrection, reported The Daily Beast.

"Trump could be charged with violating 18 U.S.C. §§ 371 — conspiracy to defraud the United States — which carries a five-year prison sentence if two or more people join forces to 'commit any offense' against the country. In their memo, legal scholars also cite how Trump and his advisers mounted a pressure campaign on then-Vice President Mike Pence that would have had him abuse his role as the overseer of the electoral certification — a clear violation of the Constitution," the website reported.

A federal judge in California already found that Trump and right-wing lawyer John Eastman had likely broken that law, and investigators have email evidence showing they knew that scheme was illegal, and the former president may have further violated that same law by trying to use former Department of Justice official Jeffrey Clark to cast doubt on the election and pressure states to use fake electors.

READ MORE: 'Worst answer I've ever heard': Republican buries DeSantis response to question about Trump crimes

"Trump could also be slapped with the same criminal charge the DOJ has used against more than 200 of the MAGA loyalists who assaulted the Capitol building during the winter insurrection: impeding an official proceeding," The Beast reported. "The massive crowd showed up at Trump’s direction following his December tweet and his D.C. speech that day calling for them to march on Congress. As the DOJ has proven time and time again in court, the rioters attempted — and succeeded — in interrupting the certification of the 2020 election results.

Smith could charge Trump with violating 18 U.S.C. § 1512(c)(2), which prohibits obstructing, influencing, or impeding "any official proceeding," which carries a 20-year prison term, but the most serious potential charge would be harder to prove and hasn't been used since the Civil War.

"Smith could try to hold Trump directly responsible for the savage violence his followers exacted on dozens of police officers — and the extensive property damage on the Capitol, which the DOJ estimated last year at $2.9 million," The Beast reported. "Legal scholars have pointed to 18 U.S.C. § 2383, which severely punishes anyone engaged in outright rebellion. It dates back to a time when the nation was at war with itself, and the Union found it necessary to snuff out any flame of violent resistance."