Ronna McDaniel, the R.N.C.’s Top Official, Plans to Step Down on March 8

The chairwoman of the Republican National Committee said on Monday that she would step down in just over a week, as former President Donald J. Trump seeks to install a new handpicked leader for the national party ahead of the general election this fall.The decision is not a surprise. The chairwoman, Ronna McDaniel, told Mr. Trump weeks ago that she planned to leave shortly after the South Carolina primary, which was held on Saturday. But she now sets in motion a new election within the party’s official body, where Mr. Trump’s preference for chair and co-chair will try to secure enough…