Outside interest group spending is set to break records for a midterm election.

The total of $228 million spent so far on this year’s midterm elections is the most in any election except 2012.

Key races which could determine control of the Senate are a major factor.

Outside spending in the race between North Carolina Democratic incumbent Sen. Kay Hagan and Republican Thom Tillis has reached $22 million, according to Federal Election Commission data compiled by the Center for Responsive Politics.

So far, approximately $13 million is pro-Democrat, while only $8 million is pro-GOP in North Carolina.

Iowa, Kentucky, Colorado and Arkansas are also among the top states for outside spending.

Spending during the 2012 presidential cycle — the most expensive one ever — topped $1 billion.