According to Yoram Shamir this poster was published by the Herut party's main adversary at the time of publication: Mapai

The "key" of Herut is a pistol and the shooter, who is assassinating a worker on his way to work, is identified by the Irgun/Herut logo printed on the cuff of the shirt

The subtext for this poster is that Herut could not be trusted to hold elected office as they would continue their violent, pre-independence habits if elected