In the months following Lincoln’s victory — he won 221 electoral votes to McClellan’s 21 — anti-abolitionist newspapers attacked his legitimacy, calling the trial another aspect of a conspiracy conducted by the president to ensure his reelection.
The commission that oversaw Ferry and Donahue’s trial recommended life in prison for the two men who sought to corrupt the election by mail. The president, who would soon be slain, approved.
https://www.washingtonpost.com/history/2020/08/22/mail-in-voting-civil-war-election-conspiracy-lincoln