Lyle Muller at the Iowa Gazette:

Run down the tallies by precinct from Tuesday’s voting [in Iowa's special senate election] and you’ll see Republican Cindy Golding holding serve in several precincts. In fact, she collected 415 more votes from people going to the polls on Tuesday, Nov. 8, than Democrat Liz Mathis received. Yet, she lost to Mathis 13,184 to 10,283, according to unofficial results pending a canvass. That’s a 2,901-vote margin.

What happened?

Mathis bagged the win with absentee and early voting when 5,422 people voted for her.'

... You could argue that rainy weather kept people from the polls but you’d have to concede that the weather would be equally bad supporters of both Mathis and Golding. Rather, Democrats had strong motivation to keep control of an Iowa Senate in which they hold a 26-to-24 majority and apparently did something about it early so that nothing that happened Tuesday would stand in their way.