Mike Johnson has spent the first 10 months of his speakership balancing the needs of the House Republican majority with the demands of his rebellious right flank. Now he faces one final legislative test before he asks GOP lawmakers to let him keep the gavel next year: A September spending fight. With a government shutdown deadline looming on Oct. 1, Johnson has two choices: Lean into conservative priorities and risk chaos weeks before the election, or work on a bipartisan basis to keep...