The chairwoman of the Republican National Committee‚ Ronna McDaniel‚ has told former President Donald J. Trump she is planning to step down shortly after the South Carolina primary on Feb. 24‚ according to two people familiar with the plans. Mr. Trump is then likely to promote the chairman of the North Carolina Republican Party‚ Michael Whatley‚ as her replacement‚ according to several people familiar with the discussions. Under the arcana of the committee’s rules‚ however‚ Mr. Trump cannot...