Trump is using executive privilege on documents relating to why the citizenship question is being asked. Mainly, it will look to conceal the fact the question and motivation is used to increase white voting power.
https://www.cnn.com/2019/06/12/politics/house-oversight-contempt-vote-barr-ross/index.html
Why do Trump and his supporters try and hide what their main motivation is? If they are truly sick of political correctness, why don't they just say they want a government and country that prioritizes white people?