One big problem of both organizations is that they have no domestic constituency. Citizens often see the job of diplomats as representing the foreign countries they work with, rather than pushing the agenda of their home country. Yet, that is seldom the case. They may often argue for going slow in going to war on slapping on sanctions in trade disputes, but that is because they understand that such actions are likely to be futile or counterproductive, although they may make Americans (or Brits) feel better for a while, until the chickens come home to roost.
In any case, those unfortunate perceptions often mean that budgets for diplomacy are among the first to get cut in bad times and among the last to be increased in good times. American lawmakers should take these British arguments to heart in considering their appropriations for the State Department.