President Trump’s bankers are walking away from him after the riot at the Capitol, deepening the uncertainty about the future of his business empire as he prepares to leave office next week. Deutsche Bank and Signature Bank have decided to end their business relationships with the president, cutting off what had been an important source of money for the Trump Organization before Mr. Trump was elected. Former Trump attorney Michael Cohen, now a bitter critic of the president, said Mr. Trump is facing a post-presidency in which voters and potential customers will judge him only on the tragedy at the Capitol.