CNN — Political leaders are generally at their strongest the moment they take office. Republican leader Kevin McCarthy is far from assured of winning sufficient support in his party to become House speaker next month. But even before the vote, his authority is already weakening by the day – in a way that could make him a speaker who is in office but not in power. The tiny GOP House majority that takes over in January, after a disappointing midterm performance, would mean a fragile governing mandate for any party at any point in American history. And the ideological struggle...