Keenan himself apparently was not supportive of Vietnam, I don't know his views on Korea, (though Korea was a US led UN operation, which must have been more acceptable to a diplomat).
We have to remember that Europe physically was unable to conduct a major war in Europe against the USSR
in the late 1940's, (military the UK could, but consent of a very war weary population, fighting against a WW2 ally, is another matter).
I suspect that before the Berlin Airlift, before Korea, the US population would not be too pleased at having just got their young men back from WW2, seeing them going off again with a new draft to boot.
Keenan served in a time before spy satellites, U-2's or SR
-71's, with little in the way of human intel assets in the USSR
was a largely unknown place, ruled by Stalin, a man who by then was likely being mentally affected by the hardening of brain arteries, that would eventually kill him.
But he was a mass murderer when in better health anyway.
A deeply paranoid place, ruled by fear, some compared Saddam to 'Hitler' during and after the first Gulf crises, wrong, he was a mini me Stalin, a tin-pot GenSec.
Stalin had willfully broken WW2 agreements across E.Europe, he had massive armed forces still largely moblised, the US didn't know it at the time, would not until 1949, but under the management of the sinister Beria (whose hobbies included driving around in his Packard car, kidnapping, raping, sometimes killing, women picked up at random), the 'Medium Machine Project', the Soviet A-Bomb, was fast becoming a reality.
Stalin probably was happy to secure an E.European buffer zone, but any sustained weakness by the Allied powers, might well have emboldened him, especially if France or Italy looked like going communist.
I think Truman played an uncertain hand very well, Attlee in the UK was firm on defence, pushed for what became NATO.
Truman came to the top job perhaps unencumbered by the experience of being POTUS in WW2, not having to regard the USSR
as a valuable ally, which FDR had no choice but to do so.
Keenan was right, he saw Stalin 'Workers Paradise' close up, in Truman he had a sensible and receptive boss.