For his part, Mr. Reines plays down his interactions with the Weiner operation, saying he is unpaid and primarily concerned with assisting Ms. Abedin, a beloved surrogate daughter to the Clintons who has faced unfriendly headlines and pointed questions about her judgment after publicly vouching for Mr. Weiner.

And at times, he cannot hide his exasperation with Ms. Abedin’s husband. On a campaign conference call hours before that news conference on July 23, Mr. Reines learned for the first time that Mr. Weiner had engaged in online liaisons after leaving Congress. He was enraged and proceeded to berate Mr. Weiner, saying he would “reach through this phone” and “pull out” his throat, adding an expletive, according to a participant on the call.

This past weekend, Mr. Reines advised Ms. Abedin against participating in Mr. Weiner’s newest campaign video, which was being filmed at the couple’s Park Avenue South apartment, itself owned by a longtime Clinton donor. Mr. Reines and Ms. Abedin agreed that she should leave her home to avoid even appearing in the background of any scene in the video, according to people familiar with their conversation, who spoke on condition of anonymity to avoid straining ties with those involved.