> In case of a President, there is a mandate from the population, because he/she was elected directly. And replacing the President is a matter of several months

> In case of a President, there is a mandate from the population, because he/she was elected directly. And replacing the President is a matter of several months at least, or, in the case of the USA, not at all. And that sends a bigger message to kill a President. We have a fairly well defined line of succession. And even if you're talking just about mandate, if the president dies the VP often takes up the dead president's mandates. Like LBJ passing major civil rights legislation the year after JFK died, or Truman following FDR pretty closely. Although Andrew Johnson did the opposite of that and Gerald Ford (not following a death, fair) didn't do anything at all.