WASHINGTON — Kamala Harris, a first-term senator and former California attorney general known for her rigorous questioning of President Donald Trump’s nominees, entered the Democratic presidential race on Monday. Vowing to “bring our voices together,” Harris would be the first woman to hold the presidency and the second African-American if she succeeds. Harris, who grew up in Oakland, California, and is a daughter of parents from Jamaica and India, is one of the earliest high-profile Democrats to join what is expected to be a crowded field.