President-elect Donald J. Trump has promised to unravel President Biden’s major legislation when he takes office next month, but Mr. Biden is hoping to salvage his most prized policies with help from an unlikely source: Republicans.With just weeks left in office, Mr. Biden and his aides have emphasized that his signature economic legislation, the Inflation Reduction Act, overwhelmingly benefits Republican districts, in the hopes that Mr. Trump would face blowback from his own party if he repealed it.The administration is also racing to award hundreds of millions of dollars in grants and finalize environmental regulations to lock in Mr. Biden’s...