Anthony Weiner's campaign for mayor plunged deeper into trouble on Thursday, as pressure mounted on him to drop out of the race and his unfavorable ratings reached an all-time high in a Wall Street Journal-NBC 4 New York-Marist poll.

Mr. Weiner provided new details of his sexually explicit online behavior, saying he exchanged lewd messages and photos with as many as three women since he resigned from Congress in 2011 for the same behavior. Mr. Weiner, who is married, has said he stopped such behavior in August 2012.

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