Context: Trump tweeted in December — "The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes", which he followed by saying "let it be an arms race."
Reality check: Trump's first order as president was on Obamacare, not the nuclear arsenal. In addition, former president Barack Obama's 2016 federal budget "laid the groundwork" for modernizing the U.S. nuclear arsenal, as Bloomberg View noted late last year.