Texas Rep. Beto O'Rourke, who's hoping to unseat Sen. Ted Cruz, has raised triple the amount that Cruz has this year, despite banning all PAC money from his campaign.

O'Rourke and campaign finance reform advocates argue that his fundraising success is in part attributable to his stance on money in politics.

Recent polling shows that independents consider the issue second only in importance to protecting the country from terrorism.

Texas Rep. Beto O'Rourke is one of just a handful of Democrats in Congress who's rejecting all donations from political action committees.

And O'Rourke, who's hoping to take Republican Sen. Ted Cruz's seat this year, has raised more money than any Democrat running for Senate from Texas in 16 years.

End Citizens United, a top campaign finance reform advocacy group, says O'Rourke's fundraising success is in part a result of a growing disenchantment among voters, including independents and swing voters, with the influence of money in politics.

"We're seeing this real ground shift among voters who are continuing to feel more and more shut out of the system," ECU president Tiffany Muller told Business Insider.

So far in 2018, the relatively little-known congressman has raised triple the amount Cruz has and is catching up to the senator in total cash on hand.

"We're far stronger than we would be otherwise," O'Rourke told Open Secrets in January of his no-PAC money pledge. "It is giving more people a reason to contribute and become part of this. They know that their five, 10 or 15 dollars is really going to make a difference. There is no PAC, there are no billionaires. This is really people."

A recent ECU poll found that 63% of Texans are more likely to support a candidate who rejects corporate special interest money. And after voters were informed of O'Rourke's position on the issue, their support for him grew by six points.

Ever since the Supreme Court's 2010 Citizens United decision, outside spending in elections has grown 800% — from $143 million in 2008 to more than $1.3 billion in 2016.

And voters are increasingly displeased with the phenomenon. In 2016, here were just a handful of candidates running for Congress who banned corporate PAC money. But this year, there are already over 70, including 15 Democratic challengers who have outraised the GOP incumbents they're hoping to unseat.

Sens. Kirsten Gillibrand and Cory Booker, both of whom will likely run for president in 2020, joined Sens. Elizabeth Warren, Bernie Sanders, and Maria Cantwell in banning corporate PAC money in February.

"There is a real wave of change coming," Muller said.

But, as evidenced by President Donald Trump's successful "drain the swamp" campaign slogan and his attacks on his former nemesis Hillary Clinton's relationship with Wall Street, voters believe both sides of the aisle are to blame for the corrupting influence of money in politics.

"Right now, voters feel like it's a pox on both our houses, both parties are way too in the pockets of special interests," Muller said, adding that independents are divided on which party has done more to reduce the influence of money in politics.

ECU's recent polling has found that reducing the influence of money in politics is the second-most important issue for independent voters, just after protecting the country from terrorism. They believe that Democrats should use their support for campaign finance reform to win crucial swing voters and independents who responded positively to Trump and Sen. Bernie Sanders' promises to fight corruption in Washington.

"Both Bernie Sanders and Donald Trump used this issue pretty effectively in their campaigns," Muller said. "We know that some of those areas that Trump over performed in are areas where they really respond to this messaging."

On Thursday, ECU will announce its endorsements of seven additional candidates, all of whom are Democratic challengers running for Congress: Gary Trauner in Wyoming, Tom Malinowski in New Jersey, Kathy Manning in North Carolina, Liz Watson in Indiana, Lauren Baer in Florida, Rick Neal in Ohio, and Matt Morgan in Michigan.