Mr Boyle added that, regardless of left or right alignment, think tanks had similar unity in their approach to the peace process.
He said: “Frankly this is just not a divisive issue in the US. It’s a settled one.”
The lawmaker also criticised Mr Johnson’s then government, where Ms Truss was serving as Foreign Secretary, stating he was “really isolating Britain from all of its traditional allies”.
Mr Biden is fiercely proud of his Irish ancestry, and frequently speaks about his great grandfather’s experience with the British.
He said: “When my great grandfather got on a coffin ship in the Irish Sea, expectation was, was he going to live long enough on that ship to get to the United States of America?
“But they left because of what the Brits had been doing. They were in real, real trouble. They didn’t want to leave. But they had no choice.”