“You can lose people through death – and you can lose them while they’re still alive,” David Horowitz says.

The conservative author and activist is no stranger to losing friends over his political views. As his autobiography “Radical Son” details, the one-time leftist theoretician angrily rejected liberalism in the wake of a friend’s murder by the Black Panthers. His reaction cost him friends, allies and, for a time, even members of his own family.

Now, in “A Cracking of the Heart,” Mr. Horowitz examines his sometimes strained relationship with one of his daughters, Sarah. Born in 1964 with Turner syndrome, Sarah stood less than 5 feet tall, had poor hips and a weak heart, the last of which killed her in 2008. The book recalls the struggles and triumphs of her life – and reveals Mr. Horowitz’s regrets about how he let his political stridency drive father and daughter apart.

“This book was therapy for me; it was a remembrance of my daughter and her extraordinary courage,” Mr. Horowitz says in a recent phone interview. “It’s a lesson to all of us who complain about much lesser frustrations and obstacles that we face. We often feel utterly defeated by them. This book should inspire people. Her life should inspire people to face those problems and not let [the problems] get them down.”

Heartened by the reaction he received to the eulogy he delivered at Sarah’s funeral, Mr. Horowitz decided to write a book that would bring her extraordinary story to life and give others a glimpse into her world.

“A Cracking of the Heart” is also a tale of family struggles, a reminder that blood is more important than whatever political differences may come between us. Mr. Horowitz is a fire-breathing conservative whose confrontational style often comes across as abrasive; his daughter, meanwhile, attended a liberal synagogue and traveled to Iowa to support Barack Obama’s presidential bid.

“Consider that these are your children, and remember your parents and the influence that they had on you,” Mr. Horowitz would advise others who sense family bonds fracturing under the weight of clashing worldviews. “Even when they are rebelling, even if they seem to be embracing values or views that are alien to you, look inside them for your influence and use that as a point of connection.”

Mr. Horowitz relates in “A Cracking of the Heart” that Sarah was often reluctant to share her writings with him. After her death, Mr. Horowitz dove into those writings – including poems, an unpublished novel and writings about her personal life – in order to find out what he could about his daughter.

He learned about more than just his daughter, however. In the course of researching the book, Mr. Horowitz also discovered that there were lessons he could have taken from his daughter’s views.

“My daughter was very generous with homeless people even though she had no money,” he says. “She would always give change to the homeless, and of course, as a conservative, at first I reacted and said that these people have substance abuse problems, they should be taken care of, they should be institutionalized.”

Then he came across a journal entry from his daughter in which she wrote about being approached by a once-homeless woman who had since pulled her life together. The woman thanked Sarah for her kindness during a rough patch and said that she had never forgotten the help.

“I realized then that we may have our policy positions about homelessness, but the reality is that … it would be worth it, even if there’s only one person that you help – even if there’s just a chance of there being one,” Mr. Horowitz says. “So my daughter really taught me a lesson there.”

He just regrets that she had to die before he was able to learn the lesson – and hopes her life can be an example to others.

“It’s impossible to read about my daughter without becoming a more compassionate, better person,” he says. “And I hope also that since we all have to endure terrible losses – they’re part of the process of life, really – that people will get strength from my book and find comfort in it.”