In 2016, outside groups, not candidates, spent the most in 27 races

On her way to winning a Nevada Senate seat in 2016, Democrat Catherine Cortez Masto spent almost $19 million; her Republican opponent, then-Rep. Joe Heck, paid out nearly $12 million. Their combined spending of over $30 million was among the highest in the nation.
Source: In 2016, outside groups, not candidates, spent the most in 27 races