Phyllis McGuire, lead singer of the McGuire sisters, the primly conservative middle-class trio that peaked from the early to late ’50s, has died at age 89.

The culture that loved and celebrated the McGuire sisters (and particularly their tidy, caressing, milk-fed signage) has long since passed into history, so why is her death of anything more than anecdotal interest now? Four words: Chicago mobster Sam Giancana.

In 1960 McGuire and Giancana were introduced in Les Vegas by Frank Sinatra. They quickly fell in love and had a long-running affair that lasted until his murder in ’75.

Their liason was part heart but mostly dough, or so one presumes. Phyllis was Sam’s “mistress”, and he “took care of her” blah blah you know the drill. But it was so weird that a woman who had fronted one of the most antiseptic, family-friendly singing trios in U.S. history, a group that stood for Midwestern wholesomeness and white-picket-fence flowerpot culture in the same region as Doris Day and Debbie Reynolds in their youthful prime…it was so bizarre that Phyllis had decided to lie down with one of the biggest mafia reptiles around, and stayed with him through thick and thin, and never broke confidence when she was subpeona’ed in ’65.

On top of which Phyllis was a Republican. How else to interpret the fact that of the five U.S. Presidents the McGuire sisters performed for, four were righties — Richard Nixon, Gerald Ford, Ronald Reagan and George H. W. Bush?

How do you square the murderous goombah swagger of Sam Giancana (who reputedly had some connection to JFK’s murder), and late 20th Century American conservatism?

Answer: They both offered women security and comfort in exchange for submission and obedience, and Phyllis, like any good mafia wife or gah-gah girlfriend, willingly obliged.

Retro Kimmer tells their saga with a fair amount of color.

You also need to watch Summertime, a 1995 HBO movie about the McGuire-Giancana affair — took a lot of liberties, indulged in fantasy, conveyed slivers of the truth.