The medieval Assassins failed to overthrow any regime and ended as hired hitmen

Evidence

A crucial feature of the medieval Assassins is their total and final failure. They did not overthrow a single regime; they did not seize power in any Muslim country of any importance. They continued to carry out an occasional assassi­ nation but, eventually, they became less like zealots and more like hired hitmen, until they were finally extinguished in the 13th century, in Iran by the Mongols, in Syria by the Mamluks. Obviously, one should not draw too close a parallel between the medieval Assassins and their modern successors, but the ignominious end of the Assassin endeavor may carry a lesson. — Bernard Lewis, From Babel to Dragomans, 575