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The promise is enforceable. The charity can argue "detrimental reliance". He made a verbal promise, he took actions in furtherance of his alleged plan to donate, the charity took actions in reliance upon his promises and actions, and as a result they were materially damaged.
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Notsure I can. This is so simple. While there was no consideration "paid" by the charity to him, they never the less had a reasonable right to rely on him, and they acted on that reliance, and they were damaged by him.