Los Angeles (CNN) Republican Rep. Duncan D. Hunter is running a brazenly anti-Muslim campaign against his Democratic opponent, a Christian who is the son of a Mexican-American mother and Palestinian father.

The ugliness has unfolded in one of the most conservative congressional districts in California, where Hunter, a hard-charging former Marine who served three combat tours in Iraq and Afghanistan, is trying to hold on to his seat after being indicted on federal corruption charges for the alleged misuse of campaign funds.

The race in California's 50th District between Hunter, the son of a long-revered congressman, and his Democratic opponent, Ammar Campa-Najjar, who is estranged from his father and was raised by his Mexican-American mother in California, is one that Democrats never really believed was winnable after Donald Trump beat Hillary Clinton in the district by 15 points.

But Hunter's dual-pronged strategy of running against the "deep state" and what he alleges is a corrupt Department of Justice and then painting his youthful challenger as a national security threat has made the campaign a fascinating test of political survival in rapidly changing eastern San Diego County.

In Hunter's latest salvo in a district where many voters are active and retired military, he sent a piece of campaign literature billed as a "security alert" to voters from three retired generals that once again draws attention to Campa-Najjar's Middle Eastern roots and the potential "dangers" of electing him to Congress.

The letter notes that Campa-Najjar's father was involved, until recently, in "Yasser Arafat's PLO," and says voters should be alarmed by the fact that the Democrat's paternal grandfather helped plot the attack on Israeli athletes at the 1972 Olympic Games in Germany. Though Campa-Najjar is estranged from his father and never met his grandfather, Hunter argues that by electing him, Californians would be putting troops and secret US military plans at risk.

Hunter's missive asserts that Army, Air Force, Marine and special operations are "undertaking military missions against terror in the Middle East even as you read this letter. Their locations and movements are highly secret ... except to Congresspersons who have a right to see classified information."

"If Democrat Candidate Ammar Campa-Najjar should get elected and sees secret information on U.S. military operations that would endanger members of his Najjar family in the Middle East, would he compromise U.S. operations to protect his relatives, the Najjars?" the mailer asks. "We would not bet the lives of our troops on the gamble. We hope you wouldn't either."

In an interview Monday, Campa-Najjar noted that he has strongly condemned the involvement of his grandfather, who died many years before he was born, in the violence at the Olympics.

Campa-Najjar, 29, noted that his father has spent only two weeks in the United States since 1995, and spoke publicly recently about his desire for peace between the Israelis and Palestinians.

"It's backfiring on him; it's desperate," Campa-Najjar said of Hunter's efforts to tie him to terrorism.

The youthful former Obama administration aide noted that he had been cleared by two federal background checks -- the first when he worked as an intern in the White House in 2013 reading letters sent to President Barack Obama and the second in 2016 when he became an aide in Obama's Department of Labor. Those comprehensive FBI background checks, he noted, included an exploration of his family history and relationships.

"His dad and my dad aren't running for Congress this time around. It's me and him," Campa-Najjar said of Hunter. "The narrative arc that he's trying to create just isn't true in the eyes of law enforcement. The Justice Department, law enforcement, the FBI, have made decisions on both of us. They cleared me to work at the White House and they indicted him."

"This is a bootstrapping district," Campa-Najjar added of eastern San Diego County, an area that is becoming increasingly diverse because of the high cost of living along the coast. Voters place a "high premium on personal accountability," he said, "and Hunter's cardinal sin this election has been his refusal to understand personal accountability -- demonstrated by him blaming the DOJ, blaming his wife, blaming me, blaming dead people that I never met, blaming an estranged father. It really reeks of desperation."

In his initial statement responding to the mailer, Campa-Najjar asserted that "While Hunter has no human sense of personal accountability, voters understand his family is not responsible for his actions, and I'm not responsible for my family's actions."

Campa-Najjar's campaign dismissed the mailer as part of the "xenophobic and race-baiting" campaign that Hunter is running, and called on Republican leaders to condemn it. Democratic US Sens. Kamala Harris of California and Elizabeth Warren of Massachusetts and independent Sen. Bernie Sanders of Vermont have all condemned the rhetoric.

Hunter's campaign did not return a request for comment.

Presumably because his seat looked safe, Hunter, one of the first congressmen to publicly endorse Trump, had largely ignored Campa-Najjar's efforts to engage him for much of the year. In the spring, Campa-Najjar, a former Obama field director, easily won the endorsement of the California Democratic Party and then edged out the other Democrats in California's top-two primary.

In a clear sign of a tightening race, Hunter has ratcheted up his attacks on Campa-Najjar's Palestinian heritage in recent weeks -- namely by running an ad charging that Campa-Najjar was trying to "infiltrate" Congress.

"He's used three different names to hide his family's ties to terrorism," the Hunter ad says. "Ammar Campa-Najjar: A risk we can't ignore."

At an event last month before a group of GOP women, Hunter claimed that Campa-Najjar had changed his name "from Ammar Yasser Najjar to Ammar Campa-Najjar ... so he sounds Hispanic."

"That is how hard, by the way, that the radical Muslims are trying to infiltrate the government," Hunter said, according to a recording of the event obtained by the Times of San Diego.

Campa-Najjar's mother, Abigail Campa, who's Catholic, issued a retort in Spanish on Twitter explaining that she had raised her son in San Diego as a single mother.

Campa-Najjar has taken the attacks in stride, pointing a flood of donations in the two days after Hunter was indicted.

Hunter set up a legal expense trust earlier this year, but he also has been forced to divert tens of thousands of dollars from his campaign account for his legal bills as he fights the charges against him.

In the third quarter, Campa-Najjar raised $1.4 million -- far more than Hunter's $132,000. Heading into the final stretch of the race, Hunter had $247,000 in cash on hand to Campa-Najjar's $685,000.

One of the groups that have come to Campa-Najjar's defense is J Street, which endorsed him because he supports a two-state solution as part of achieving peace in the Middle East. The group has also noted Campa-Najjar's unique perspective on the issue because he lived in Gaza as a child for four years before fleeing the violence there and returning to San Diego County, where he was born.

JStreetPAC, which has endorsed about 180 House and Senate candidates this cycle, helped the Democratic candidate raise nearly $50,000 -- with many of those donations coming after the PAC sent an email to donors about Hunter's attacks.

"We find these attacks on Ammar to be disgraceful and very obviously rooted in bigotry and fear mongering," said Logan Bayroff, director of communications at J Street. "They quite clearly have no foundation in fact. They are not about policy. They are not about security. They are about trying to fear-monger on the basis of Ammar's Arab and Hispanic heritage."

"He thinks he can tap into the fears of voters," Campa-Najjar said Monday, "but there have been Republicans who have been coming to support me, not in spite of the attacks but because of his attacks. It's a fundamental misunderstanding of the character of our district."