North Korea could challenge the ability of the Ground-based Midcourse Defense system to protect the U.S. homeland as soon as 2025, according to an assessment by U.S. Northern Command -- revealed by a lawmaker and verified by a top Pentagon official -- that anticipates continued advances in Pyongyang's long-range missile program. This public disclosure comes as the Defense Department is grappling with plans to replace the Redesigned Kill Vehicle -- a failed warhead project intended for fielding by 2023 to...