STANFORD, Calif. — Hillary Clinton is doing what Republican rivals now say they took far too long to do: Taking Donald Trump seriously. In interviews and foreign policy addresses this week, the Democratic front-runner has worked to undercut Trump’s credentials in the wake of deadly bombings in Brussels. Her goal is to transform the voters’ vision of the bombastic reality TV star into a potential commander in chief with his finger on a nuclear trigger — an image her team believes will repel voters in November. Clinton is casting herself as a calm harbor in a stormy world, frequently mentioning the need for “steady hands.” The comment is a clear reference to Trump with the implication he’d never fill that need. In a speech Wednesday Stanford University, Clinton called for “strong, smart, steady leadership,” arguing that recent comments from Republicans Trump and Texas Sen.