Writing in the Telegraph, Mr Gardiner said Mr Biden is following his predecessor Barack Obama’s “lacklustre ‘leading from behind’ doctrine”.
He then said Mr Biden agreeing to the summit “was a mistake”, with no “conceivable benefit” for the US.
The former aide wrote: “Putin is not a pragmatist like Mikhail Gorbachev, the Cold War leader who worked with Ronald Reagan and Margaret Thatcher to bring an end to the Soviet Empire.
“He is a cold-blooded killer, schooled in the murderous and uncompromising mindset of the KGB, and he should never have been granted a meeting with the US president while there are still Russian troops in Georgia and Ukraine.”
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