Using the market as a measure of success, President Trump has something to boast about: The 5.5% gain for stocks during his first 100 days in office is third-best of any president since World War II.Saturday marks Trump’s 100th day in the White House. The return of the Standard & Poor’s 500 stock index under Trump since Inauguration Day is better than the past three U.S. presidents, better than Barack Obama in 2009, George W. Bush in 2001 and Bill Clinton in 1993, according to data compiled by financial research firm CFRA. The 9% jump in the early days of John F. Kennedy’s presidency in 1961 ranks No. 1.