U.S. Sen. John McCain has served as a senator from Arizona for nearly 30 years. But for McCain to win reelection in November, the war hero-politician will first have to survive his own party's primary. 

McCain will square off against challenger Kelli Ward in Arizona's Tuesday Republican primary. Ward, until recently a relatively unknown state senator in Arizona, has made headlines in the weeks leading up to Tuesday's primary with a series of controversial attacks against McCain. Meanwhile, pundits speculate that the closer-than-expected primary and general election tests McCain faces in 2016 have prevented the iconic politician from more pointedly criticizing GOP presidential nominee Donald Trump.

John McCain U.S. Sen. John McCain will face a primary challenger in Republican Kelli Ward in the Arizona Republican primary on Aug. 30, 2016. Photo: Alex Wong/Getty Images

Ward has represented Arizona’s Fifth Legislative District as a state senator since 2013. She resigned from office in December to focus on her U.S. Senate campaign six months after announcing her candidacy on July 14, 2015. The 47-year-old doctor of osteopathic medicine was born in Virginia and attended Duke University in North Carolina before heading to the West Virginia School of Osteopathic Medicine for medical school and A.T. Still University in Arizona for a master's degree in public health.

Ward has used her status as a physician to criticize Obamacare. While Ward acknowledges McCain's status as an American war hero and longtime public servant, she has accused him of being too much of an "establishment" candidate who has not done enough to curb government spending and is too close to Democrats like presidential nominee Hillary Clinton. Ward has been very critical of McCain's inaction on immigration reform and alleged support of "amnesty." She supports Trump's plan for a border wall across the U.S.-Mexico border. 

Most polls of likely Republican primary voters show McCain ahead of Ward, but not by much. Some polls show McCain up only by low double digits, while others have had him as close as two points ahead of Ward. Ward has even come out on top in some surveys. Ward has denied that the polls accurately reflect Arizona voters, telling Fox News' Sean Hannity that McCain "definitely is showing the desperation in the campaign," adding, "If this polling were true, why would he bother?"

In the lead-up to Tuesday's vote, Ward has garnered attention for a series of controversial attacks against McCain. 

On July 11, Kelli Ward published an attack ad on her Facebook page outlining how McCain's policies line up with those of Clinton. The ad was a near exact copy of a 2008 Republican primary attack ad against McCain from then Republican rival Mitt Romney. In response to criticism of the ads' similarities, a campaign spokesperson for Ward said, "Mitt Romney got it right, If the shoe fits, wear it. The substance is still the same. Some things never change."

More recently, Ward attacked McCain for his age, questioning his health. Ward told POLITICO last week that the soon-to-be 80-year-old senator may not live to finish out another term.

"I’m a doctor," Ward said. "The life expectancy of the American male is not 86. It’s less."

The McCain campaign dismissed the age criticism as an act of desperation from a losing campaign. 

On Saturday, Ward wrote off McCain's attendance at the grand opening of a playground in honor of Kayla Mueller, the 26-year-old hostage from Prescott who was murdered by Islamic State militants, as a last-ditch ploy for votes.

Though McCain may choose to take a dismissive tone towards Ward's attacks, critics argue that the reason he has thus far refrained from more harshly criticizing Trump or revoking his endorsement of the GOP nominee — something anti-Trump conservatives have urged him to do for months — is a fear of alienating far-right conservatives who might bail on him for Ward if he turns on Trump. McCain has at times denounced specific comments, such as the GOP nominee's attacks against Gold Star family members Khizr and Ghazala Khan, but he still endorses the businessman.