Are activist investors short-term traders or in it for the long term? It is the question of the moment as nearly $200 billion has poured into the coffers of activists with names like Icahn, Ackman and Peltz, among others. Last year, as a group they put some 200 companies in their cross hairs and replaced 19 chief executives, according to the law firm Sidley Austin, putting pressure on virtually every board in the country to pay attention to this vocal class of shareholders. If you listen to C.E.O.s and politicians on the stump these days, you would get the sense...