Democratic candidates in key Senate races hold a cash advantage over their Republican opponents in an increasingly competitive battle for control of the upper chamber. 

In 13 Senate races that have been rated as competitive by the nonpartisan Cook Political Report, Democratic candidates had topped fundraising by their GOP rivals as of Wednesday. 

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“If Democrats take back the Senate ... the fundraising advantage challengers built early on, largely enabled by grass-roots small-dollar donors, will also play a large part in that victory," Jessica Taylor of the Cook Political Report wrote in a final pre-election analysis.

ActBlue, a nonprofit technology company that was founded in 2004 to channel small-dollar donations to Democratic candidates and liberal groups, processed about $1.5 billion in contributions from the beginning of July through the end of September. That's about the same amount it processed for the entirety of the 2018 election cycle.

It also far exceeded the $623.5 million raised by its Republican equivalent, WinRed, during the same period.

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“I think Democrats with ActBlue are way ahead," Sen. Ron Johnson, who is up for re-election in 2022, told The Hill. "Hats off to them, they did a really good job. We’re just behind." 

According to data from the Federal Election Commission, Democrats have outraised Republicans in 13 of 15 competitive Senate races: Arkansas, Alabama, Arizona, Colorado, Georgia, Iowa, Kansas, Kentucky, Maine, Michigan, Montana, North Carolina and South Carolina.

In South Carolina, for instance, Democrat Jamie Harrison has raised a staggering $107 million, compared with Republican incumbent Sen. Lindsey Graham, who's brought in about $72 million.

The two exceptions are Texas and Georgia. 

Republicans are fighting to hold a slim 53-47 majority in the Senate as Democrats target several GOP-held seats they believe are competitive. In order to take back the Senate, Democrats would need to pick up three additional seats and win the White House.

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Although Republicans are hoping to win back the Alabama seat held by Democratic incumbent Sen. Doug Jones – who is considered to be one of the most vulnerable senators – Democrats are going after GOP senators in a growing number of states, including Maine, Colorado, Georgia, Iowa, Montana, North Carolina and South Carolina. 

Still, the fundraising strength does not necessarily indicate a blowout victory for Democrats on Tuesday. 

Even in races where Democrats stand little chance of winning -- like in Kentucky, where former Marine fighter pilot Amy McGrath is challenging Senate Majority Leader Mitch McConnell -- they have raked in more cash than their competitors. Between July 1 and Sept. 30, McGrath brought in nearly $36.9 million, while McConnell raised about $15.6 million. A forecast from FiveThirtyEight gives McGrath just a 5% chance of winning. 

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Some Democrats have pushed to make radical changes that have the potential to reshape the country should they win control of the White House and both chambers of Congress, including eliminating the Senate filibuster, granting statehood to Puerto Rico and Washington, D.C., and expanding the Supreme Court.

"As far as the filibuster, I'm not busting my chops to become majority leader to do very little or nothing," Senate Minority Leader Chuck Schumer, D-N.Y., said during a recent interview with MSNBC. "We are going to get a whole lot done. Everything, everything is on the table."