Sen. Rob Portman won the endorsement of retired four-star Gen. Barry McCaffrey Friday, and his campaign announced that the former "drug czar" for former President Bill Clinton cut an ad for him that is set to run immediately.

McCaffrey praised the Ohio Republican in the ad as one of the "finest public servants" he's met, and lauded him for his work to help fight the ongoing heroin epidemic, which has become a major issue in Ohio. Portman co-sponsored the Comprehensive Addiction and Recovery Act, a bipartisan bill aimed at prevention and treatment for opioid addiction.

"Sen. Portman has played an essential role in national leadership. Sen. Portman did the hard work. He was able to pull together people from both parties and get the CARA Act passed to deal with this wave of heroin addiction that's sweeping the country," McCaffrey said in the ad. "We need people like Rob Portman. He's one of the finest public servants I've ever met."

"I've been in some tough battles, so I know a strong leader when I see one," McCaffrey added in a statement, adding that he is "happy" to back him for reelection.

"I am honored to have General McCaffrey's support — he's an American hero, a decorated soldier, and a proven leader," Portman said in a statement. "It was a privilege to work with General McCaffrey to help fight our country's drug epidemic, and our country is better because of his service."

The ad will run statewide beginning on Friday and is part of the campaign's $15 million ad buy, which started in June.

Portman holds a nearly 6-point lead over former Ohio Gov. Ted Strickland, according to the latest RealClearPolitics average, a race that could determine whether Republicans hold onto the Senate majority next year.