Hillary Clinton maintains a 5-percentage-point lead over Donald Trump in the presidential race despite the FBI report on her email practices and mounting clamor for change by a restless electorate, a new Wall Street Journal/NBC News poll has found.

Mrs. Clinton held a 46%-41% margin over her Republican rival heading into the parties’ national conventions, unchanged from a Journal/NBC News survey taken last month. That previous poll was before the Federal Bureau of Investigation report that called the Democrat “extremely careless”...