The White House and the nation’s most prominent charities are embroiled in a tense, behind-the-scenes debate over President Obama’s push to scale back the nearly century-old tax deduction on donations that the charities say is crucial for their financial health.

“It’s all castor oil,” said Diana Aviv, president of Independent Sector, an umbrella group representing many nonprofits. “And the members of the nonprofit sector I represent don’t want any part of it. It’s a medicine we’re not willing to drink.”

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