If there’s one sure sign someone is suffering from Trump Derangement Syndrome, it’s using the death of a former president as a platform to attack the current commander-in-chief.

Leftist late-night host Stephen Colbert did just that on “The Late Show” on Monday night.

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In what was meant to be a tribute to the recently deceased George H.W. Bush, Colbert showed his true colors and took his anti-Trump obsession to new heights.

The comedian began by calling Bush 41 “the last president of the Greatest Generation.”

Footage was then shown of H.W. Bush being rescued by a submarine crew in 1944 during World War II after he was forced to evacuate his own plane.

Bush became one of the youngest aviators in the United States Navy after he joined the service at the age of 18 in 1941. He served his country until 1945.

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Colbert used this military experience as an excuse to attack President Donald Trump.

“The closest our current president has gotten to a submarine is a five-dollar footlong,” the comedian said of the current president.

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Colbert then went back to praising Bush. The comedian said the former president was not a “bitter person” and he then showed a clip from a segment of “The Colbert Report” — which Colbert once hosted on Comedy Central — from Iraq, where Bush had a special message for troops serving their country.

“Back in World War II, the USO used to send us great big stars like Marlene Dietrich, Lauren Bacall and the Rockettes,” Bush said in the 2009 clip.

“I’m just saying, this Stephen Colbert guy better have great legs.”

Colbert ruined his own tribute to Bush by adding in a Trump dig.

What is the point?

He attacks Trump each and every night, so why would he do so during a segment meant to highlight Bush?

Though he attacks the president and conservatives endlessly, Colbert — by contrast — is plenty nice to his friends on the Left.

It shows how truly obsessed with the president the extreme leftist critics have become. They can’t even celebrate the life of an American president, during a period of mourning and appreciation, without bringing themselves and everyone else down with low-blow critiques aimed at the current president.

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Colbert showed some great footage of Bush and had some positive things to say about the man’s life, but Colbert ruined what could have been a unifying moment by acting like a partisan jerk.

Though he attacks the president and conservatives endlessly, Colbert — by contrast — is plenty nice to his friends on the Left.

Check out part of a recent puff piece interview he did with Michelle Obama, the former first lady, in the clip below: