Forget the Koch brothers. Eliana Johnson of National Review Online shines a light on the real big-money heavyweight in the 2014 elections.

The Republican wave in 2010 may, in the end, be what saves Democrats in 2014.

Four years ago, when Harry Reid thought he and his Senate majority were vulnerable, Democrats swooped into action, creating a super PAC known as Commonsense Ten, which devoted itself to protecting embattled Democrats and expanding their majority in the Senate. In late July of that year, it secured a landmark ruling from the Federal Election Commission that allowed it to rake in unlimited donations from corporations and labor unions.

In the following year, 2011, Commonsense Ten renamed itself the Senate Majority PAC and Reid’s top political strategist, Rebecca Lambe, took the reins. If the Senate Democrats fighting for their political lives survive the November elections, they will have Reid, Lambe, and her PAC to thank. It has ramped up its spending more than tenfold since 2010, to more than $35 million this cycle from about $3.2 million four years ago, to protect the party’s incumbents and the Democrats’ Senate majority.

“Democrats have come back significantly into the outside spending game in a way that they weren’t doing,” says Steven Law, the president and chief executive officer of American Crossroads, which has since 2010 been the dominant super PAC on the right.

Senate Majority PAC has given Democrats some distinct advantages, allowing them to attack Republicans early in the campaign season on explicitly political terms. Super PACs are required to disclose their donors, but they are permitted to raise unlimited funds and to run ads urging citizens to support or oppose political candidates. The Senate Majority PAC, which has outraised every super PAC on the right (the closest is American Crossroads, which has hauled in $13 million), was up with ads against Arkansas representative Tom Cotton and Senate minority leader Mitch McConnell as early as June 2013. By November of the same year, it was rallying around embattled North Carolina senator Kay Hagan.