The trading platform Kalshi issued a three-year suspension to the candidate, Laurie Buckhout, and fined her nearly $2,600. Ms. Buckhout said she had made a “dumb mistake.”

© Chris Seward/Associated Press

A legal dispute over the future of Kalshi, Polymarket and others has drawn in the Trump administration, the president’s son and nearly every state attorney general.

© Ricardo Tomás