Several Republican and super PAC ads under fire by watchdogs, fact-checkers and rights groups for false accusations.

This article has been corrected to say that Duncan Hunter was indicted on allegations he illegally used $250,000 in campaign funds, not $250m as previously stated.

A number of midterm campaign ads have attempted to link Democratic candidates in tight Congressional races to “terrorism”.

Slated for November 6, the midterm elections are largely viewed as a referendum on President Donald Trump. Voters will decide all 435 seats in the House of Representatives, 35 seats in the Senate and 39 governorships in US states and territories.

Although campaign ads attacking opponents’ records are common from candidates on all sides of the political spectrum, a number of ads – many funded by a leading Republican super PAC – have drawn a backlash from watchdogs, fact-checkers and rights groups.

Most recently, California Republican Duncan Hunter, who has been indicted on charges of violating campaign finance laws, has drawn criticism over ads his campaign ran attacking his opponent’s Palestinian background.

Hunter, who has held California’s 50th district’s House seat for the last decade, was indicted in August on charges of using upwards of $250,000 of campaign funds for personal purposes.

In late September, Hunter was leading Ammar Campa-Najjar, the Democratic challenger and former Obama White House aide, by eight points. But a more recent poll, conducted by the University of California, Berkeley for the Los Angeles Times, shows Hunter’s lead thinning, putting the Republican at 49 percent and Campa-Najjar at 47 percent.

With the race tightening, the increasingly embattled Hunter’s campaign released controversial ads attacking Campa-Najjar, a 29-year-old Palestinian Mexican American progressive.

In one ad last month, Hunter inaccurately implied that Campa-Najjar was a “radical Muslim” who sought to “infiltrate” Congress.

The Republican incumbent also called Campa-Najjar a “security threat”, attempting to link the Democratic challenger to his deceased grandfather, who was involved in planning the deadly 1972 Munich Olympics attack on Israeli athletes.

A Washington Post article fact-checking Hunter’s claims deemed them false.

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Campa-Najjar, who was born 16 years after his grandfather, Muhammed Yussef al-Najjar, was killed by Israeli agents, says he was raised by his Mexican mother and identifies as a Christian.

Mike Harris, Hunter’s spokesman, told Al Jazeera via email that the “national security concerns regarding our opponent have absolutely nothing to do with the fact that he has Palestinian heritage, it has absolutely everything thing to do with the fact that Ammar Campa-Najar has current, existing relationships with the PLO and CAIR.” Harris did not elaborate.

Campa-Najjar recently told voters that “there are two candidates in this race: One of us was indicted by the FBI, the other one was cleared by the FBI to work at the White House”, Vox reported.

Trump campaigned on promises to crack down on Muslims, pledging to stop Muslims from entering the US and at one point proposing a database to monitor Muslim Americans. After entering office, Trump introduced a controversial travel ban that blocked entry to the US for citizens of several Muslim-majority countries.

Accusations of ‘terrorism’ links

Hunter’s attacks on Campa-Najjar are part of a broader wave of Republican ads alleging their challengers are linked to “terrorism”.

In Ohio, Representative Steve Chabot, an outspoken supporter of Trump’s travel ban, has attempted to link his opponent, Aftab Pureval, to “terrorism” owing to the 36-year-old Democratic challenger’s former employment at a law firm that settled terrorism-related lawsuits against Libya.

Pureval was not involved in the settlements, which were approved by Congress, the New York Times reported.

Many other ads, which have been produced by a Republican super PAC, the Congressional Leadership Fund, have also been criticised by fact-checking watchdogs and civil rights groups.

In New Jersey, the Congressional Leadership Fund targeted Tom Malinowski for arguing that Guantanamo Bay detainees should receive due process while he was Washington director of Human Rights Watch.

In one ad, the Super PAC claimed Malinowski “criticised America for waging war against al-Qaeda”.

In September, Monmouth University released a poll putting Malinowski eight points ahead of his Republican opponent, incumbent Leonard Lance in the state’s 7th district.

And in Virginia, Abigail Spanberger, a former undercover CIA operative, was targeted over her former part-time teaching job at the Islamic Saudi Academy in Alexandria.

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“Spanberger doesn’t want us to know that she taught at an Islamic school nicknamed ‘Terror High,’ a terrorist breeding ground,” the ad claims.

She currently leads her incumbent Republican opponent, Dave Brat, 47 percent to 42 percent in Virginia’s 7th district House race.

A spokesman for Spanberger’s campaign dismissed the ads in a statement to local media, saying they were “laughable considering Abigail’s record of service in law enforcement, at the CIA and in our community”.

Super PACs are barred from directly coordinating with campaigns.

The Council on American-Islamic Relations (CAIR), a Muslim civil rights organisation, has criticised several other instances of anti-Muslim sentiment throughout the midterm elections.