President Trump’s former campaign adviser Roger Stone spent Labor Day vilifying John McCain in a pair of social media posts, denouncing the recently deceased Arizona senator as treasonous and corrupt.

Mr. Stone lashed out at McCain in separate Instagram posts Monday, a day after the Vietnam War veteran and lawmaker was laid to rest at the U.S. Naval Academy in Annapolis, Maryland.

“Enough already,” Mr. Stonecaptioned a photograph he shared on Instagram of a People magazine issue honoring McCain. “I knew John McCain Well since he was In the House. A bitter cranky and vengeful man responsible for the death of 134 servicemen in on the Deck of the USS Forrestal and as corrupt as the come,” Mr. Stone wrote.

“John McCain was epically corrupt, and a cranky mean spirited p—k,” Mr. Stone wrote in a subsequent Instagram post captioning a photograph of an article published by The New York Times. “His passing of the Russian dossier to the FBI was a fraudulent act of treason and he will get his just reward from his maker,” he added.

Months before being captured in Vietnam and held for years as a prisoner of war, McCain survived a fire that killed over 100 fellow service members stationed abroad the USS Forrestal aircraft carrier in the Gulf of Tonkin. McCain’s critics have smeared him as being complicit in the tragedy, but fact-checking sites including Snopes have found those claims to be false.

More recently, McCain acknowledged that he gave the FBI a copy of the so-called “Steele dossier” that alleged connections between Mr. Trump and Russia — a subject of an ongoing investigation being conducted by special counsel Robert Mueller on behalf of the Justice Department.

“I did what duty demanded I do,” McCain wrote in his recently published memoir, “The Restless Wave.”

A longtime Republican strategist, Mr. Stone, 66, advised Mr. Trump’s presidential election campaign in 2015. He subsequently raised eyebrows over his contacts in 2016 with Guccifer 2.0, an internet persona operated by Russian military officials, and his claims of being in touch with Julian Assange, the publisher of the WikiLeaks website responsible for releasing internal Democratic Party documents in the lead-up to Mr. Trump’s election.

In an interview conducted after The Washington Times first reported that Mr. Stone exchanged private Twitter messages with Guccifer 2.0 during the presidential election, McCain called for bringing him before investigators.

“Obviously I think he and others need to be questioned,” McCaintold CNN last March.

Roger Credico — one of at least eight people contacted by Mr. Mueller’s office closely associated with Mr. Stone — plans to appear before the special counsel later this week.