Or, and bear with me here, he was so massively, impossibly corrupt, incompetent, and idiotic, that not only did he never have the intention to 'drain the swamp' but was the very bogmother himself. Then, even if he wasn't, lacked the most basic of capabilities to do it anyways because he's the kind of person that would have difficulty solving a 1×2 Rubick's Cube.

He had 4 years to drain the swamp with control of 2 wings of our government, so obviously we have nothing to worry about now.