Huma Abedin seemed like a sure thing in a Clinton White House. But is the latest FBI inquiry a scandal too far?

In the summer of 2013, Hillary Clinton had just left the State Department and returned to New York. She planned a quiet year, basking in sky-high approval ratings and enjoying a respite from the media

spotlight as she laid the groundwork for a second presidential run.

Then Carlos Danger happened.

Anthony D. Weiner, the husband of Mrs. Clinton’s closest aide, Huma Abedin, was running for mayor of New York when news broke that he had continued to exchange lewd messages with women online after the practice cost him his congressional seat. This time, he used the embarrassing Spanish-inspired moniker.

The tawdry story line and Ms. Abedin’s closeness to Mrs. Clinton made the events explode far beyond New York, dragging Mrs. Clinton’s name into messy headlines about penis pictures, Mr. Weiner’s descriptions of his sexual appetites and his online paramour named Sydney Leathers.

Now, with Mrs. Clinton seemingly on the cusp of winning the White House, Mr. Weiner, who once described himself as “a perpetually horny middle-aged man,” has pulled her into another drama. Federal investigators looking into his sexual messaging with an underage girl stumbled upon thousands of emails potentially pertinent to the F.B.I. inquiry into Mrs. Clinton’s private email server.