Sen. Kirsten Gillibrand (D-N.Y.) will announce Tuesday evening during an appearance on The Late Show with Stephen Colbert that she is launching an exploratory committee to raise funds needed for a 2020 presidential bid. Why it matters: Gillibrand is the latest candidate and the third woman to join what is expected to be a large and diverse Democratic primary. Gillibrand has opposed 94.6% of President Trump's executive branch nominations, more than any other Senate Democrat.Go deeper: Track which candidates are running in 2020