A senior Republican senator with a reputation for not rocking the boat in Donald Trump’s Washington spent Wednesday doing just that, issuing blistering criticisms of the president for his continued attacks on the late Sen. John McCain.

Sen. Johnny Isakson, a Georgia Republican, appeared on a political talk show on Georgia Public Broadcasting on Wednesday afternoon to denounce the president’s most recent comments about the senator and Vietnam war hero who died seven months ago.  

“It’s deplorable what he said,” Isakson said. “It will be deplorable seven months from now if he says it again.”

In a series of weekend tweets, Trump mocked McCain for being “last in his class” at the U.S. Naval Academy and accused him of fueling the Russia investigation. “I was never a fan on John McCain’s,” Trump said at a Tuesday press conference, “and I never will be.”

Isakson, who is the chair of the Senate’s Veterans Affairs committee, has been a reliable supporter of Trump and his agenda. He did not, for example, join the dozen GOP senators who joined Democrats to block the president’s national emergency declaration last week. He has mostly avoided direct confrontation of Trump, but has also spoken up at various points when the president’s actions have drawn broad criticism, such as his declaration that there were good people on “both sides” of the 2017 neo-Nazi rallies in Charlottesville, Virginia.

But Trump’s inability to resist disparaging McCain has made Isakson his most determined critic among Senate Republicans, at least on this front. He said the president’s long-running attacks on McCain showed an inappropriate “lack of respect” for the late senator’s military service. “If my kids started talking about John McCain was not a hero, or things like that, they’d have a serious conversation with me and I’d have it with them,” said Isakson.

“The weight of my words is proportionate to how few I use,” Isakson said. “I am not a big word user. But I am on this one.”

Most of Isakson’s colleagues have been far more circumspect, save for Sen. Mitt Romney (R-UT) who tweeted he “can’t understand why the president would, once again, disparage a man as exemplary as my friend John McCain.”

Even Sen. Lindsey Graham (R-SC), who called McCain his best friend, avoided criticizing Trump. He issued tweets on Sunday about McCain saying “nothing about his service will ever be changed or diminished,” without directly acknowledging what prompted his defense.

Similarly, on Wednesday Senate Majority Leader Mitch McConnell paid tribute to McCain as a “patriot” but did not mention Trump or his attacks. Isakson said Wednesday that other Republican senators should weigh in, if they think it’s appropriate.

The Georgia senator teased his remarks with an interview published Wednesday morning by The Bulwark, an online publication associated with the “Never Trump” movement. “When the president is saying that that he doesn’t respect John McCain and he’s never going to respect John McCain and all these kids are out there listening to the president of the United States talk that way about the most decorated senator in history who is dead,” said Isakson, “it just sets the worst tone possible.”

Isakson served in the Army National Guard during the Vietnam War but did not see combat there, unlike McCain, who spent years there as a prisoner of war. “I want to elevate John,” Isakson said. “John was better than I am, and I know it. John was the best of my generation. John McCain was and is a great human being.”