As the battle heats up for control of Congress, primary contests across the nation are drawing large pools of money from long distance donors who are shaping the outcome of key races.

Nearly 2,700 candidates are vying for one of the 435 U.S. House seats up for grabs in November. So far, they've raised more than $800 million for their campaigns, according to the latest data from the Federal Elections Commission. Though it's still early in this year's midterm cycle, roughly two-thirds of that money has come from outside those candidates' districts.

Of the 41 seats in the four states holding primaries Tuesday, candidates in more than half those districts have collectively raised more than $1 million.