His role in American involvement in Vietnam?

I think the entire American establishment - possibly the whole of the Western World - bought in to the Domino Theory. So not entirely Eisenhower's fault. Just as easy to blame it all on Churchill and his Iron Curtain speech.

US aid to (South) Vietnam was minimal prior to 1960 and was mostly non-military. More than once Charles DeGaulle appealed to Eisenhower to intervene on the behalf of the French and Eisenhower declined. Kennedy was the one who ramped up involvement by sending military advisers to help the South Vietnamese. It was also said that Kennedy was under pressure by the French who were being asked to place ICBM's in their country at a point in time where France was very fearful of Soviet expansionism in Western Europe. That the price of basing missiles in France would include helping it reclaim lost territory in SE Asia formerly known as French Indo-China. Eisenhower certainly was not a hawk when it came to Vietnam.