North Charleston, S.C.—Tim Scott, the lone Black Republican senator who showcases himself as a “sunrise” conservative, is expected to launch his historic yet underdog bid for president on Monday. Scott will join an expanding field of GOP contenders looking to knock out Donald Trump, the former president who remains a muscular frontrunner despite qualms that he isn't the best to challenge President Joe Biden. But Scott and his team see this race as a marathon, and exude a confidence based on a combination of his biography and fundraising despite hovering at roughly 2% in primary polls. The South Carolina senator...