The loyal opposition in a democracy is the concept that one can be opposed to the government without being opposed to the constitution or the political system. In time of war , the loyal opposition referred to the party not holding the office of President and meant that it would cooperate fully and without reservation in the war effort.
It is comforting to know that the Republicans are not opposed to the constitution but I doubt this is what they mean when they call themselves the loyal opposition. Do they mean that they will cooperate fully and without reservation in the pursuit of two wars in Afghanistan and Iraq. Hardly, they keep second guessing every move the Obama administration makes. So what are they talking about?
My guess is that it is the work of some strategist who sold the leaders on the concept that "the loyal opposition" sounds much more noble then "the minority party". It is also provides cover when they rebuff any attempts of bipartisanship by the Democrats. "As long as you do it my way we'll get along. We don't oppose the constitution but we oppose your right to govern. We are the loyal opposition!"
(cartoon from Chattnooga Times Free Press - Bennett)