Harry Reid and his fellow Democrats have made a campaign fetish of denouncing the Koch brothers and other rich conservative donors for allegedly buying elections. This turns out to be one of the great misdirection plays of all time because big money might save the Democratic Senate majority in November.

The untold story of this campaign is that Democrats are trouncing Republicans on fund-raising, fueled by those "big donors" and "special interests" they claim to despise. That Democrats remain competitive in so many close Senate election races despite low incumbent approval ratings is in large part a function of this spending advantage.

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The Democratic Senatorial Campaign Committee has so far this cycle raised $111 million, or $30 million more than the National Republican Senatorial Committee. The DSCC has spent or reserved nearly $42 million for this fall in TV advertising—55% of it in Iowa, Colorado and North Carolina. The $23 million it will spend in those three key states—which could determine Senate control—is $4 million more than the NRSC will spend across the country.

After the DSCC, the biggest spender has been Mr. Reid's very own Senate Majority PAC. Run by former Reid aides, this Super PAC's only mission has been to trash Republican challengers to take their approval ratings as low as those of Democratic incumbents. The group has already raised more than $32 million, with $16.5 million in TV ads reserved through Election Day.

To continue reading Karl Rove's column in the Wall Street Journal, click here.

Karl Rove joined Fox News Channel as a political contributor in February 2008. He also currently serves as a columnist for the Wall Street Journal. Mr. Rove helped organize the political-action committee American Crossroads. His latest book is "The Triumph of William McKinley: Why the Election of 1896 Still Matters" (Simon & Schuster, 2015). Follow him on Twitter @KarlRove.