Well
a phrase is easy enough to come up with - but I doubt that it would actually mean what I want it to mean.
「忠実な反対側」...はダメでしょう。^^v
The meaning being that although (people / parties) are opposed to the government party's policy they respect the position of authority of the government under law and in turn are respected by the government as having the best intentions for the country.
<- man that's a horribly long sentence. ^^;
It may have been observed,
in theory, in the UK but the practise is usually different. I don't know if the concept even registers in the US