Democrats are spending tons of last-minute cash in their bid to seize the House from the GOP

Democrats are leaving nothing to chance in the final leg of the midterm election campaign, outspending Republicans by a wide margin in the parties' battle for control of the House.

With less than a week left before Election Day, campaign cash is flooding into battleground congressional districts around the country as Democrats seek to win back control of the House.

In just the last week alone, political action committees have shelled out more than $340 million in so-called soft-money spending, mostly on campaign ads favoring one party over another. These outside spending groups aren't limited in how much they can spend, as long as they don't coordinate directly with a candidate.

The bulk of that cash — more than $200 million — is being spent in the 30 districts rated as "toss-up" by the Cook Political Report.

Most of those seats in toss-up districts are held by Republicans. But in the final weeks of the campaign, Democrats are outspending their GOP rivals by more than 2-to-1. Five of those toss-up races are in California, where outside spending has flooded those battlegrounds. More than $50 million has been spent since last Wednesday, according to the latest campaign finance data provided by the Center for Responsive Politics.

In those five races — for California's 10th, 25th, 39th, 45th and 48th districts — Democrats are outspending Republicans by more than 4-to-1. Most of that money is paying for campaign advertising, and most of it is negative. Voters in the most competitive battleground races have been inundated with television ads since Labor Day, and the pace is expected to continue through the weekend into the final days of the campaign.

The number of negative ads aired from Labor Day through Oct. 25 was up 61 percent over the 2014 midterms, according to the Wesleyan Media Project. Nearly 569,000 attack ads were broadcast during that period, up from the 2010 record of nearly 450,000.

Here's how soft-money spending has been flowing in the last week to the hottest races in the country:

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