The Democratic congressman challenging Sen. Ted Cruz for US Senate in Texas has shattered fundraising records. Viral videos of O'Rourke speaking have captivated progressives across the country and sparked talk about him as a potential 2020 presidential candidate. And his campaign's innovative approaches on the digital and organizing fronts could become a model for Democrats everywhere in the years ahead.

But less than three weeks from November's midterm election -- and just four days before early voting starts in Texas -- polls still consistently show him trailing Cruz in the high single digits.

O'Rourke will get a national audience and a chance to shift the race Thursday night when CNN hosts a 7 p.m. ET town hall meeting with O'Rourke moderated by Dana Bash in the border city of McAllen.

In recent days, O'Rourke's tone has turned much more confrontational -- underscoring that he has ground to make up and little time to do it. O'Rourke began airing direct-to-camera television ads attacking Cruz on immigration and health care Wednesday. The new spots came the morning after he assailed Cruz as "dishonest" in a debate in San Antonio.

"It's why the President called him 'Lying Ted,' and it's why the nickname stuck -- because it's true," he said.

His newly negative approach shows the challenge facing O'Rourke: Texas is a red state that President Donald Trump won by 9 percentage points in 2016. Running an idealistic campaign hadn't closed the polling gap. But attacking Cruz on policy issues -- the terrain more comfortable to Cruz, who has relentlessly cast O'Rourke as too liberal for Texas -- could alienate conservative voters, some of whom O'Rourke needs.

"When an unconventional candidate becomes conventional, that's when they get split like a cantaloupe," Cruz campaign manager Jeff Roe said after Tuesday night's debate. "He doesn't have a second act. He's been making a liberal bed, and tonight he tucked himself in."

O'Rourke is the only candidate participating in CNN's town hall. Cruz declined multiple invitations to appear back-to-back with O'Rourke. Last week, Cruz challenged O'Rourke to turn Thursday's town hall into a debate, but the two campaigns were unable to reach agreement on a format change.

A different Democratic approach to Texas

O'Rourke launched his campaign on the promise that he would never accept money from political action committees -- even those friendly to progressives' interests. The pledge, along with viral videos of O'Rourke defending NFL players who protested during the National Anthem, skateboarding and more, turned him into an online, small-dollar fundraising dynamo. And O'Rourke shattered every record for a Senate candidate when, in the third quarter of 2018, he hauled in more than $38 million.

The money, which will allow him to outspend Cruz in an expensive state to advertise, is one reason Democrats believe O'Rourke is more competitive than previous Democratic disappointments in Texas, where the party has been shut out of statewide office since 1994.

Another reason: O'Rourke has visited all 254 of the state's counties, drawing massive crowds in small cities and towns where event-goers said they haven't seen a statewide Democrat since Ann Richards, the governor in the early 1990s.

But that might not be enough -- particularly to turn out Latino voters, a constituency Democrats have to reach to win in Texas.

In 2016, Latinos made up 28% of the voting-eligible population in Texas but just 20% of the electorate -- people who actually turned out to vote -- according to the Census's Current Population Survey. In midterm elections, Latinos have made up an even smaller share of the Texas electorate. Recent polls have shown O'Rourke leads with Latinos, but is not seeing the kind of surge in interest in the midterm elections from them that Democrats have seen from other constituencies, like women.

O'Rourke's innovative digital operation

If O'Rourke is going to outperform the polls on Election Day -- and reach constituencies that Democrats have often ignored in Texas -- it'll be because of his digital and organizing efforts, both of which are led by veterans of the Bernie Sanders presidential campaign.

In the field, O'Rourke's campaign has embraced "distributed organizing" -- a strategy that channeled the ground troops backing Sanders' presidential campaign in places where no paid staffers were on the ground. Rather than peppering the vast state's smaller cities and towns with field offices, O'Rourke field director Zack Malitz and his organizers have launched hundreds "pop-up" offices, which are actually spaces like super-volunteers' houses and garages.

To raise money, O'Rourke has also followed Sanders' small-dollar approach.

Three consultants -- Shelby Cole, ad strategist Liz Bennett and graphic designer Camilo Caffi -- were the core of O'Rourke's early digital team. The group expanded over the summer when the three were hired by Middle Seat Digital, where digital organizing strategists Kenneth Pennington and Hector Sigala have also worked on O'Rourke's campaign.

Bennett's ads built O'Rourke's massive email list. And Cole -- who originally sold O'Rourke on the vision of a campaign that could raise massive amounts of money online as long as he didn't rely on a cookie-cutter digital effort -- runs the email program.

O'Rourke's emails are much longer and more personal than most political fundraising solicitations. He never uses popular tactics such as fake deadlines, sky-is-falling warnings, or "final notices" intended to scare potential donors into giving.

"If you quote me describing Shelby and Liz, please use the word 'geniuses,' because that's what they are," said Mike Nellis, the digital consultant for California Sen. Kamala Harris.

"I don't think they get the credit that they deserve," he said. "At least for Democratic consultants, they should be household names."

O'Rourke has also filmed content for his digital ads, rather than repurposing TV spots, and also has a vast archive of Facebook livestreams that have turned into ads.

A recent study from the Wesleyan Media Project found that between May 31 and September 3 of this year, 53% of O'Rourke's campaign ad spending was on digital -- a vastly higher share than other major Democratic candidates.

Facebook's political advertising archive shows O'Rourke has run more than 5,800 ad variations -- including 460 that are active now -- on the platform. Google's political ad report shows O'Rourke is the only candidate to spend more than $1 million on Google ads this year. Democratic digital strategists also said O'Rourke has been especially effective at advertising on YouTube, which is often an afterthought for candidates.

Tara McGowan, a Democratic strategist who ran the Priorities USA super PAC's digital program in 2016 and then launched ACRONYM, credited O'Rourke's campaign for understanding the value of authenticity in reaching donors. One ad she pointed out was a Facebook fundraising solicitation that features O'Rourke, sitting on a doorstep, explaining his no-PAC strategy and saying, "I need your help one last time. ... I'm counting on you, and I'm grateful."

"Too many candidates and party committees still today lean way too closely to outdated assumptions of how to win elections and lean on a very old, outdated model," she said. "You don't pick a very small, targeted group of people and meet them one-on-one or over broadcast television and move the needle just enough to win."

Sharpening his Cruz attacks

His impressive fundraising and innovative organizing approaches might not be enough, though, in a contest where Cruz has mastered the one-line political attack and O'Rourke has, until recently, been hesitant to swing back.

Cruz in Tuesday night's debate warned that electing O'Rourke would lead to "two years of a partisan circus and a witch hunt on the President."

He also mocked O'Rourke's more combative approach.

"It's clear Congressman O'Rourke's pollsters have told him to come out on the attack," Cruz said.

Cruz's effort to align himself with Trump is a bet that O'Rourke will fail to turn out substantial numbers of new voters. A CNN poll out Tuesday found that Trump's approval rating with all adults in Texas is 41%. But it's much higher -- 49% -- among likely voters.

Trump plans to visit Texas on October 22 -- the day early voting begins -- for a major rally with Cruz in Houston.