'Let it be an arms race.'That's how President-elect Donald Trump clarified a tweet he sent Thursday which said the U.S. must 'strengthen and expand' its nuclear arsenal, a remark that set off warnings and calls for explanation. He then spoke on the phone with MSNBC's 'Morning Joe' co-host Mika Brzezinski, who reported on air Friday morning that the president-elect said, 'Let it be an arms race. We will outmatch them at every pass.'