Sentence:  Fearful of inviting a military showdown with the West which they could <WSD>not</WSD> win , the Communists seek to undermine Western power where the nuclear might of the West is irrelevant - in backwoods guerrilla skirmishes , in mob uprisings in the streets , in parliaments , in clandestine meetings of undercover conspirators , at the United Nations , on the propaganda front , at diplomatic conferences - preferably at the highest level . 
Meaning of the word marked with <WSD> tags:  negation of a word or group of words