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The answer to your question would be the same in every U.S. jurisdiction: An attorney has a duty to their client to act competently in any legal representation. If the attorney's failure to respond results in a judgment against their client, and that judgment is more adverse to the client than would have been true had the attorney responded to the petition, then the attorney would be in breach of duty, and the cause of the client's injury. That is the textbook definition of professional negligence (malpractice): (1) duty to client; (2) breach of duty; (3) actual cause of injury; (4) reasonably foreseeable cause of injury (legal cause); and (5) damages.
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