Ohio Sen. and Republican vice presidential nominee J.D. Vance has intensified attacks on Minnesota Gov. Tim Walz, the Democratic vice presidential nominee, accusing him of dodging service in Iraq when he left the Army National Guard to run for Congress in 2005, CNN reports.

Vance claims Walz falsely asserted he served in a combat zone.

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The debate over Walz’s military record is a key issue in the race, as both parties attempt to define the relatively unknown governor. Walz, who served in the Army National Guard for 24 years, retired just two months before his unit received deployment orders to Iraq. The Harris campaign hopes his military background will appeal to voters, while Republicans seek to portray him as an out-of-touch liberal.

At a Michigan campaign stop, Vance accused Walz of abandoning his unit.

“When Tim Walz was asked by his country to go to Iraq, you know what he did? He dropped out of the Army and allowed his unit to go without him,” Vance said.

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Walz’s retirement in May 2005 coincided with his congressional campaign launch. In a 2009 interview, he explained that he left the Guard to focus on his congressional run, citing the Hatch Act, which limits political activities for federal employees.

The Harris campaign emphasized Walz’s extensive service, while the White House defended his record. This is not the first time Walz’s military record has faced scrutiny, as similar criticisms arose during his gubernatorial campaigns.

“This is someone who enlisted at 17 years old to serve his country. He was part of the Army National Guard for 24 years. This is someone who was a high school teacher, right?” said White House press secretary Karine Jean-Pierre. “A high school coach as well, who grew up in a small town in the Midwest, and so I think his bio speaks for itself, who he is speaks for himself, his record speaks for itself, and I’m just not going to say anything beyond that.”

Read more at CNN.