Republicans are growing concerned that the staffs of Donald Trump and Mike Pence are starting to feud, the latest trouble to hit a White House that has spent months battling crisis after crisis. They worry that any rift could be delaying decisions, distracting aides from their already stalled legislative agenda and could lead to more infighting and leaks, problems that have plagued the White House since Inauguration Day. A half-dozen Republicans, including four who advised or worked for Trump’s campaign or transition and are still in contact with their former colleagues, said they think the two sides are talking less,...