washington unite state ironclad commitment mutual defense among nato ally white house say thursday republican presidential nominee donald trump raise question whether would defend nato ally attack white house spokesman josh earnest decline directly address trump comment new york time say potential foes make mistake miscalculation washington readiness defend nato treaty ally u.s. commitment pledge ironclad earnest tell brief president renew commitment two weeks ago today travel warsaw poland attend nato summit u.s. 'ironclad commitment nato mutual defense white house