With primaries wrapped up in roughly 70 percent of congressional districts this week, campaign donors are beginning to turn to placing their bets on the general election.

Much of that money is coming from just a handful of the nation's richest donors, according to the latest campaign finance data.

Voters went to the polls in seven states Tuesday to pick party nominees in New York, Colorado, Maryland, South Carolina, Utah, Oklahoma and Mississippi.

So far, some $1.3 billion has been raised by 2,715 candidates for 435 House seats and 435 hopefuls in 35 Senate races. And some of the biggest checks are coming from just a handful of the wealthiest donors.

As of the latest monthly fillings, the 100 top individual donors to the upcoming House and Senate elections have contributed a combined $237 million, according to a tally of campaign finance records by the Center for Responsive Politics. Of that amount, roughly half came from just the top 12 donors on the list.