For my money, Peter Beinart spells it out clearly in his recent editorial, “Speech Impediment”:
By suggesting that Kerry – in the course of a presidential campaign – should view Bush primarily as our commander-in-chief rather than as an opposing candidate, and that he should not seek to bring him down, Miller is implying that there is something disloyal about an aggressive effort to defeat an incumbent president in a time of war. This anti- democratic vision of the 2004 election is the natural extension of the Bush campaign’s anti-democratic suggestion that John Kerry should not criticize the war in Iraq. It is the most demagogic argument of the campaign so far. A more decent president would be ashamed.