Barry Goldwater... in his retirement phase... used to say that Truman was the greatest US president. ( might have said "one of the"; it was a long time ago.)

But yeah: from their POV what was there not to like? National security state. Red Scare #2. Anti-foreigner: Russians, Chinese, etc. America -as-Empire; perpetual war for perpetual profit, gigantic military budgets$$ in peacetime. etc. etc. etc.

Bush, who supported Dewey, got called out on that.

he negotiated the International Trade Organization (which republicans refused to ratify) and he enacted GATT by executive order (because he knew republicans would not vote for that in congress either).

I am sure what makes him a president that republicans would like unless it was getting the UN to authorize an international response to the North Korean invasion of the south. That war hardly ended in victory (or defeat) so it's hard to imagine Truman looking like much of a hero there.