Elon Musk's "dual roles pose conflicts of interest so obvious that they hardly require explanation," Sen. Richard Blumenthal wrote in the letter obtained by CBS News.

The department plans to buy armored Tesla vehicles. Elon Musk, who is leading efforts to cut government spending, has won more than $13 billion in government contracts in the past five years.

It shows how some of Musk's wealth has come and was still expected to come from taxpayers before the plans were put on hold.