Can someone legally back out of a multi-million-dollar mortgage by claiming they weren't mentally capable of making the decision? That's exactly what one retired New York lawyer is asking a federal court to decide. John G. Bonomi Jr. is suing JPMorgan Chase after buying a $5.5 million waterfront mansion on Cape Cod that was already at risk of falling into the ocean. A Luxury Home With a Very Expensive ProblemThe five-bedroom, seven-bathroom home in Wellfleet, Massachusetts sat on a rapidly eroding bluff overlooking Cape Cod Bay. He wants the court to cancel the remaining $3.85 million mortgage, along with interest, damages, and attorney's fees.