As Rep. Silvestre Reyes finishes up his eighth term representing El Paso, he is facing an unusual challenge: an experienced, credible primary opponent with a respectable campaign war chest.

In his most recent campaign filing, former city council representative Beto O'Rourke raised $130,331 compared with incumbent Reyes' $204,710. A September poll by the El Paso Times showed Reyes ahead of O'Rourke by a small margin, 39 to 32 percent.

With a little more than a month to go until the May 29 primary, the battle for the Democratic nomination in the 16th Congressional District is turning into a Texas brawl. If campaign fundraising and poll numbers stay tight, then the congressional primary in El Paso could hinge on a divisive topic: the war on drugs.

Reyes, 67, has used his connections in Washington to secure endorsements from two of the country's most prominent Democrats, former President Bill Clinton and President Barack Obama. While in Congress, Reyes said he has pushed for Recovery Act money for El Paso and to keep Fort Bliss open.

O'Rourke, 39, followed a peripatetic path to politics. His father was an El Paso County judge. In the early 1990s, he attended Columbia University, then lived in a loft in New York's Williamsburg neighborhood while working at an internet start-up.

Returning to El Paso, O'Rourke started at a web design company then entered politics. In two terms on the El Paso City Council, he spearheaded development in the city's downtown, took a strong stance in favor of an ordinance providing gay and lesbian couples partner health benefits, and co-authored a book arguing for an end to the prohibition on marijuana.

The marijuana issue has emerged as a flash point in the race since Reyes ran an ad about it during the Academy Awards Feb. 26. Reyes, a Vietnam veteran and former border patrolman, repeats without apology the claim (disputed by many scientists) that marijuana is a "gateway drug" to other, more dangerous vices.

"My opponent seems to think that recreational use of marijuana is okay with him, and that's the group he hangs around with -- but it's not for me, it's not for my grandkids," Reyes told HuffPost.

"I don't want to live in a community where people think that it's okay to light up a joint and parade around elementary schools and junior highs," he added, echoing his ominous Oscars ad.

Despite Reyes' stinging attacks -- which O'Rourke, the father of three, said he found offensive -- the challenger is "not backing off my position. I have the courage of my conviction. It is clear to me that what we're doing is a failure."

"You have 10,000 people killed in the most brutal fashion in Ciudad Juarez (Mexico) in the last 10 years, without a single word from the congressman about what we can do to change the dynamic and stop the bloodshed," O'Rourke said. Marijuana is "the cornerstone of the cartel economy."

O'Rourke also pointed out that Reyes accepted a $9,500 campaign contribution from a former county official who was recently arrested on drug trafficking charges.

"There's a presumption of innocence under the Constitution that we have to respect," Reyes responded. "That money has been set aside. I'm not using that money."

He brought up a $5,000 donation from the Marijuana Policy Project and $2,500 from the Drug Policy Reform Fund to O'Rourke's campaign account.

Elsewhere in the country, border lawmakers are far from uniform in their opinions on the drug war. Some, like Reyes, are staunch proponents of ensuring marijuana stays illegal. But another prominent Democratic House member from a border district, Raul Grijalva, has co-sponsored a bill to end marijuana prohibition.

Dan Riffle, a legislative analyst at the Marijuana Policy Project, whose PAC made a donation to O'Rourke, said that "within the next few years Congressman Reyes' position will be the minority position … the folks that have been career politicians and playing this game as long as he has, they're still stuck in that war on drugs mindset."

But Riffle added that while "reporters love to write about" marijuana prohibition, it's not always a top issue within districts.

For O'Rourke, the campaign is more about issues like long waits at the border, high unemployment and federal support for Fort Bliss, a cornerstone of the region's economy. It is also about corruption.

In March, O'Rourke pounced on a report from Citizens for Responsibility and Ethics in Washington that Reyes had doled out $600,000 to family members for campaign work from his election fund. He also pointed out that the majority of Reyes' donations have come in from outside the district, while most of his have come from El Paso.

"He's dialing it in. He's content, complacent and comfortable," O'Rourke said. In Congress, he said, "the temptations are so big. The ability to abuse power is so easy."

But Reyes claimed that O'Rourke is "naive" to the ways of Washington and that his opponent is open to someday raising the Social Security retirement age.

"I'm proud of my track record, and I'm proud of the votes I take on behalf of the people of El Paso," Reyes responded. "I'm proud that my record reflects the values of the people of El Paso."

CORRECTION: The original article stated that the Medical Marijuana PAC donated to O'Rourke. The correct name is the Marijuana Policy Project (MPP).