He has used his high name ID to raise funds, mount a massive TV advertising and direct mail campaign, and tout a slew of endorsements. When the race started, Green had more than $1 million in his coffers.
His challenger, former Harris County Sheriff Adrian Garcia, who started his campaign from scratch, has been a decided underdog in the fundraising race. But he hopes a robust social media campaign can help him make up the difference in dollars and to make history, as the first Hispanic U.S. representative elected from a Houston-based district.
Despite Green’s advantages as the incumbent and having a larger war chest, a large turnout could have the biggest impact in tilting the scales — and both candidates are more than aware of that possibility.
And so Green heads into Tuesday's primary day with some anxiety.
"If you're not worried, you're not reasonable," said Green, who has served in Congress since 1993.
Initially, Garcia said there was little daylight between his policy positions and those of Green. Instead, he said at the time, his campaign was about Houston finally sending a Hispanic to the U.S. House and countering real estate magnate Donald Trump's rhetoric. But once the campaign ramped up, his charges zeroed in on Green's environmental and gun rights records.
"When I announced this campaign, it was out of anger not for Gene but for me, for standing by and allowing this to continue and saying to a friend, 'Sorry buddy, you're my friend, you'll always be my friend.'" Garcia said. "But this district needs leadership, and it needs a voice.'"
In the closing weeks of the campaign, Green has raised money at a clip of tens of thousands of dollars a day. That money has helped fund his expansive outreach efforts in the district, which stretches from north Houston to Pasadena and South Houston.
Green’s campaign has also enjoyed the support of several trade associations. Local and national Hispanic groups lined up to back Green, countering Garcia’s charges that he is a weak voice against the incendiary rhetoric of Trump’s Republican presidential campaign.
Green also has endorsements from nearly every prominent Latino elected official in the area, and from labor. His supporters say he's a tireless fighter for his constituents.
"He battles every day for the community. Not just union workers, but all workers," said Steve Flores, the president of the local Communications Workers of America chapter. The national CWA union spent at least $20,000 on radio ads for Green.
While Garcia lagged behind Green in fundraising and endorsements, he says he is confident heading into Tuesday. And with Secretary of State Hillary Clinton in the race, Hispanic turnout could climb in the district, which is 76.3 percent Hispanic. Hispanic turnout is key to Clinton’s Texas delegate campaign.
Garcia’s name could catch the eye of Hispanic voters drawn to the voting booth by the presidential race at the top of the ticket.
"We've always said, the more competitive the presidential primary, the better for us," Garcia said.
While Garcia could benefit in this way, he could also split many of those votes with a third Democrat in the race, realtor Dominique Garcia (no relation).
But Garcia isn’t just relying on a name. Citing his unsuccessful 2015 mayoral campaign, he said he’s learned to fight and to not sit back.
"In the mayor's campaign, I didn't respond as quickly as I should have, and I'm not letting it happen in this campaign."
Garcia has also been active on social media. His Twitter following is closing in on 14,000 Twitter followers. In contrast, Green heads into Election Day with a little over 200 followers.
Early voting hasn’t provided a clear indication of which candidate is holding the advantage. Operatives in both campaigns say they are encouraged, and polling is scant.
"Green's strength is rooted in four decades of elected office, his donor base outside the 29th District and his name identification with voters," said Beto Cardenas, a Houston political donor. Cardenas is a past contributor to both candidates over the years, including to Garcia's current campaign.
"Adrian's strength is centered on his service to others, his familiarity with the needs of the voters in the district and his ability to bring together those with differing views and assets to deliver for his constituents," he added.
Whatever happens Tuesday, it will not be easy for the two to mend the friendship they shared before Garcia surprisingly launched his challenge against Green. Green said the friendship that dated back to Garcia's childhood is over.
"You don't treat friends that way," Green said.
Green takes particular issue with Garcia’s criticism of his environmental policy — the Garcia campaign has branded him “Benzene Gene.”
"He's blaming me for children having cancer on the east side," Green said. "That's not the way you endear yourself to someone."
Garcia repeatedly maintained he still considers Green a friend and has not let up on his charges that Green sides with big business over the health of his constituents.
Green, for his part, has taken his own shots at Garcia. He called Garcia's campaign a "Hail Mary" and faulted the former sheriff's record in a December interview with The Tribune.
Garcia said such comments show his opponent is worried about the race.
"For being there as long as he has and supposedly having an incredible track record, why would he have to stoop that low to keep a seat?" he asked. "All of these are indicators that Gene is in trouble, and I am going to win."
Alexa Ura contributed to this report.