Technically, the 14th Amendment saved Davis' ass, but in reality, there was little desire on the part of the North to punish confederates once they has surrendered. People wanted to bring the nation back together and hanging southern leaders wouldn't have advanced that agenda. Lee and all of his troops, were given a parole by Grant at Appomattox. Grant followed Lincoln's advice to him to "Let them up easy." Andrew Johnson, a southern man himself, wanted Lee tried. Grant told Johnson he would resign from the army and raise hell in the press if he went after Lee and broke Grant's word. Do you recall Lincoln's 2nd inaugural?
With malice toward none, with charity for all, with firmness in the right as God gives us to see the right, let us strive on to finish the work we are in, to bind up the nation's wounds, to care for him who shall have borne the battle and for his widow and his orphan, to do all which may achieve and cherish a just and lasting peace among ourselves and with all nations.
That lunatic stage actor who I saw you praising the other day killed the best friend the south had at that point. Reconstruction would have been much different and better for the south, and for the nation, had Lincoln lived.