Knight was instrumental in formulating and winning passage of the GOP's tax reform law last year. She was the deputy to former National Economic Council director Gary Cohn, who left the White House early this year.
Short worked for Vice President Mike Pence and a group affiliated with the conservative Koch Brothers' political operation, before entering the White House.
The staff change marks the latest shakeup to the West Wing. Trump's administration has set records for turnover of senior officials, with more than 60 percent of those with the title of assistant to the president departing in the first 18 months.
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