This is GPS, the Global Public Square. Welcome to all of you in the United States and around the world.

I'm Farid Zakaria coming to you live from New York.

Today on the show Horror in Pittsburgh, 11 people are dead after an anti-Samite shooting rampage at the city's tree of life synagogue.

I'll discuss the massacre with a panel. Then this week's other news on foreign policy with Samantha Power, Michael Hayden and Stephen Hadley.

But first, here's my take. This is a sad week for America, one of the saddest that I have ever witnessed.

First a series of bombs directed at a former president and other public figures, then an act of horrific terror in a house of worship.

We seem to have crossed lines and broken barriers of decency. The attack on the tree of life synagogue strikes me as particularly tragic.

One of the most extraordinary features of modern American life has been the integration of its Jewish community.

For over 2,500 years Jews have been vilified and persecuted everywhere and then came America and Israel.

Two places where Jews could breathe easily and live safely.

In turn, in this country, Jews have been deeply patriotic and productive Americans, scaling the heights of achievement but also becoming civic leaders, philanthropists and good citizens.

And yet, we have seen an unmistakable rise of anti-Semitism in recent years. Now this. What does it say about America?

The two events of this week are quite different and most importantly, let's be clear, the responsible parties for the violent acts are the people who perpetrated them.

But they have taken place against a backdrop. First, there's been decades of increasingly heated and nasty political rhetoric.

People are moved to action by what they believe, by the words, thoughts, ideas they are surrounded by.

John Maynard Keynes once said that madmen in authority who hear voices in the air are distilling their frenzy from some academic scribblers of a few years back.

And Donald Trump has spoken harshly about his opponents. But he has not had a monopoly on this kind of talk. Democrats have done their share of demonizing.

Now, I think this particular story does have a beginning, at least in the modern era. It's well told most recently in the Atlantic by M. K. Coppins.

In 1978, Newt Gingrich, a fiery young congressional candidate from Georgia, explained to a group of college Republicans what he called one of the great problems we have in the Republican Party.

We don't encourage you to be nasty. Coppins writes that Gingrich set out to remedy this defect.

And when he made a push for Republican majority in the House a decade later, he sent cassette tapes and memos to party members across the country instructing them on how to speak like Newt.

He suggested labeling the Democrats with words like sick, pathetic, lie, anti-flag, traitors, radical, corrupt.

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