The argument in the given text is that the US president cannot sustain his legacy because of the slow progress of his initiative, i.e. ‘securing nuclear materials’, which, in other words, means that if he can speed up his initiative, he can have a lasting glory. So, the underlying assumption here is that whether one has a lasting glory or not depends on how fast their initiatives progress. The assumption comes out only in statement 2. Hence, statement 2 is the right answer.