MICHAEL GOODWIN: US feels divisive in 9/11 aftermath as memories of unity fade.

Yet few anniversaries of 9/11 have been as fraught with troubling emotions as today’s. From the vantage point of the 18th anniversary, it is unfortunately true that the worst day in American history forged the last great moment of national unity.

The mourning and sense of common purpose that were so distinct then seem as if they happened in a different country in another century. Now our nation is not just polarized. It is fractured.

“I’ve never seen it like this,” an elderly friend told me recently. “I’m afraid of what’s happening to our country.”

She is not alone. And while the 9/11 attack certainly didn’t cause our bitter divisions, its ramifications are among the powerful forces still shaping our dangerous world.

I don’t remember any “unity” lasting more than a few weeks, or months at best.