(S (S (NP (NP (BASENP (DT The) (NN head)) (PP (IN of) (BASENP (DT the) (NNP United) (NNPS States) (NNP National) (NNP Nuclear) (NNP Security) (NNP Administration)))) (PRN (COMMA ,) (BASENP (NNP Linton) (NNP Brooks)) (COMMA ,))) (VP (VBZ has) (VP (VBN been) (VP (VBN forced) (S (VP (TO to) (VP (VB resign) (PP (JJ due) (PP (TO to) (BASENP (NN security) (NNS issues))))))))))) (PERIOD .))