He's the special prosecutor in charge of the investigation behind the hijacking of Air Force Two, the Vice President's private plane, as well as a conspirator in covering up Cyrus Beene's involvement in said crime. Even though Mencken may seem like just another run-of-the-mill legal type lurking in the background, his death could have severe ramifications.
In his second appearance this season, we learn Mencken is participating in this sham of an investigation to get back at President Mellie Grant for her failure to deal with the gun laws that got his son, Adam, killed in a mass mall shooting. Even though nobility lies at the heart of his deceit, characters of this ilk — that is, ones introduced to do the dirty work of others — usually end up as collateral damage. While Cyrus and Olivia are shooting at each other, he's bound to find himself in the crossfire.
Mencken is by far the most obvious casualty since the treason charges that stem from his office are the show's main conflict. Obviously, his elimination doesn't stop the subpoena process of Mellie and Olivia, but his death muddles the issue enough to create an opening for Quinn Perkins and Associates to swoop in for the victory.
Chances of a season finale death: 100 percent