Complex sentence: Since 1990 he has worked in the newspaper's Washington Bureau and was the White House reporter during the last two years of the presidency of George H.W. Bush and the first two years of Bill Clinton.
Split into simpler sentences: Since 1990 he has worked in the newspaper's Washington Bureau. He was the White House reporter during the last two years of the presidency of George H.W. Bush and the first two years of Bill Clinton.