CORRECTED-Trump threats complicate negotiations for whistleblower to testify to Congress

U.S. President Donald Trump's public attacks on the unidentified whistleblower at the center of a Democratic-led impeachment inquiry are complicating negotiations for the person to testify to Congress, according to three people familiar with the matter.Trump has suggested the whistleblower committed treason, prompting concerns among Democrats on the U.S. House of Representatives Intelligence Committee that testifying could raise the risk of exposure.White House officials were not immediately ava