Ann has done a signal service trying to rehabilitate McCarthy, and Horowitz doesn't disagree with her on that point. His point, which I think is a fair one, is that not all Democrats were traitors in the sense Ann implies. I've actively followed American national politics since the late '50s, and remember the Army-McCarthy hearings earlier on. As a graduate student in history, modern US was one of my exam fields, although not my primary specialty. So, not only did I live through the period in question, I have studied it academically. Based on both my personal recollections and academic reading, I think Horowitz is right, and Ann has painted with too broad a brush.
I think a more true book could have been written which suggested that many Democrats from elite backgrounds who were not communists, simply couldn't believe anyone from their sort would actually be a communist. A similar class blindness was also evident in England. Further, I think there was a relatively quiet until the late '60s struggle for the soul of the Democratic party, which was won by those who were truly sympathetic to communism. The old anti-communist Democrats who rallied behind Truman in 1948 and carried the banner through the LBJ era may have been somwhat foolish, but they were not traitors, regardless how misguided they were on domestic policy.
I am no fan of the Kennedys. I think of them as St. John the Martyr, Robert the Dead, and Edward the Pretender. John Kennedy, at least, was probably more in that school than not. I'm not so sure about Robert, whom I regarded in life as an exceptionally dangerous and unscrupulous man. At the risk of sounding ghoulish, I think the nation was far better off that he was removed from the political scene. Teddy, of course, is loved by the left as a Useful Idiot, too stupid to realize how he is being manipulated.
Being naturally repulsed by all thing Kennedy I never read much about them specifically. Though I never ascribed genius level intelligence to any of them do you really think old Teddy is actually stupid and a pawn? do you think he has advisors and staff that guide his postitions? I just assumed he was a radical liberal of moderate/average IQ with a strong drive to destroy our country.
Ann makes a valid point that Roosevelt, Truman, Kennedy, and Johnson were all soft on Communism from the point of not being willing to either strategically negotiate or fight wars to win.