Huma Abedin, Hillary Clinton’s most trusted confidante, is increasingly becoming a central figure in the email scandal that’s haunting her boss on the campaign trail, as Republicans and federal judges seek information about Clinton’s communications while she was running the State Department. The 2016 Democratic front-runner on Monday told a federal judge that Abedin — long considered her boss’s keeper and even dubbed her “shadow” — had her own email account on Clinton’s now infamous home-brewed server, “which was used at times for government business,” Clinton acknowledged. That’s an unusual arrangement, even for top brass at the State Department. Abedin...