John Howard gave us the "non-core promise". Now Tony Abbott has added a new category to the hierarchy of political commitment with his "pledge in blood" to repeal the carbon tax, which passed the lower house of Parliament yesterday (unless, of course, that was just an "unscripted remark" made "in the heat of verbal combat".)

Abbott’s hyperbole has certainly attracted the headlines, but it betrays a curious tactic. By using such uncompromising rhetoric, Abbott has left himself no room to move if repealing the nascent scheme becomes legally impossible or popularly unpalatable.