A bitter feud is escalating between Republican Sen. Rand Paul and Donald Trump’s top border official, injecting uncertainty into Congress’s attempt to pass the administration’s signature policy bill this month.

Stephen Miller arrived on Capitol Hill Thursday to brief Senate Republicans on the White House's border wall request.

GOP frustration bubbled over in a closed-door meeting with senators and White House deputy chief of staff Stephen Miller on Thursday morning, Axios has learned. Why it matters: The border has long been a unifying issue for Republicans.