Treasury Secretary Steven Mnuchin and Office of Management and Budget Director Mick Mulvaney were on Capitol Hill this week sounding the alarm on the debt ceiling. That’s the limit on how much debt the government can rack up. Mnuchin and Mulvaney said Congress might have to lift or suspend the debt limit sooner than planned. Mulvaney said that’s because tax revenues are coming in slower than he expected. Why is there a revenue shortfall?

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