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(CNN) —  

Donors sent a wave of fresh money this month to North Dakota Sen. Heidi Heitkamp, one of the Senate’s most endangered Democratic incumbents, in the days after she voted to oppose Brett Kavanaugh’s ascension to the Supreme Court.

Heitkamp collected an eye-popping $12.5 million during the first 17 days of October, more than three times the $3.8 million she raised during the entire July-to-September fundraising quarter. Donors who give in small amounts fueled about 60% of her individual contributions.

The cash tsunami underscores how the contentious process surrounding Kavanaugh’s confirmation has stirred activists. Republicans say they too have seen a donor outpouring in response to the drama of the Kavanaugh hearing and the razor-thin vote to send him to the nation’s high court.

The GOP-controlled Senate confirmed Kavanaugh this month following a high-profile hearing and FBI investigation into allegations of sexual assault lodged against him. Kavanaugh has denied any wrongdoing.

Heitkamp announced her opposition to Kavanaugh in early October. By voting no, she bucked conventional wisdom and risked her re-election prospects in a state that backed President Donald Trump by a wide, 36-point margin in 2016. She faces GOP Rep. Kevin Cramer on November 6.

But October’s cash windfall left Heitkamp with $11.1 million stockpiled for the final sprint to Election Day, campaign reports filed Thursday night with the Federal Election Commission show. Cramer had less than $1 million remaining.

Throughout the election cycle, fundraising has surged for Democrats in some of the most competitive congressional contests. And some of the Republican Party’s wealthiest donors are unleashing big sums in the final days of the campaign to counter that advantage.

GOP donors contributed nearly $22 million to the Senate Leadership Fund between October 1 and October 17, the new filings show. The super PAC, aligned with Senate Majority Leader Mitch McConnell, can raise and spend unlimited amounts, provided it does not coordinate its decisions with the candidates it supports.

Chris Pack, the super PAC’s spokesman, said Republican donors were “fired up” by Democrats’ “underhanded tactics” in the Kavanaugh confirmation process. That’s helped the political action committee work to fill the gap “in the massive fundraising disparity between Democrat and Republican candidates in this cycle,” he said in an email.

Senate Leadership Fund donors in October included investment firm founder Charles Schwab and his wife, Helen, who contributed a total of $4 million, and hedge-fund billionaire Paul Singer, who gave $500,000.

In all, the super PAC has collected more than $121 million through mid-October, surpassing the amount the group raised during the entire two years of the 2016 election cycle.

CNN’s David Wright contributed to this report.