Republican Sen. Ron Johnson (Wis.) said Sunday that he would prefer the Internal Revenue Service (IRS) undertake a “robust” investigation into the leak of President Trump’s tax returns, days after the president sued the agency for $10 billion over the disclosure.

President Donald Trump is suing the IRS and Treasury Department for $10 billion, as he accuses the federal agencies of a failure to prevent a leak of the president's tax information to news outlets.