Republicans looking to rewrite the U.S. tax code are taking aim at one of the foundations of modern finance—the deduction that companies get for interest they pay on debt.

That deduction affects everyone from titans of Wall Street who load up on junk bonds to pay for multibillion-dollar corporate takeovers to wheat farmers in the Midwest looking to make ends meet before harvest. Yet a House Republican proposal to eliminate the deduction has gotten relatively little sustained public attention or lobbying pressure.

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