At a book signing in Detroit this morning, I ran into a wonderful family whose son is serving right now in Afghanistan.

I asked them how he was doing.

"Very well," they said. "He's always upbeat."

When I inquired about the media coverage of the war there and in Iraq — and whether he was catching any of it — they offered this revealing comment:

"He just can't believe it," his dad said. "There's a lot of good they're just not reporting," his dad quoted his son as saying.

I thought of that conversation after reading this Al Qaeda (search) bigwig letter to a top deputy.

"Things may develop faster than we imagine," Aymen al-Zawahiri (search) writes.

He explains that Americans are getting fed up with the negative news out of Iraq and goes onto note that, "the aftermath of the collapse of American power in Vietnam, and how they ran and left their agents, is noteworthy."

He talks of how the U.S. has a habit of cutting and running and implies we'll likely be cutting and running soon again.

The letter clearly lays out al-Zawahiri's long-term goal: Get the Americans out, bring an Islamic authority in and then take the war to Iraq's secular neighbors, before the ultimate clash with Israel.

He seems eerily patient — perhaps because he senses we are not.

He seems resolute. We seem divided.

It's not our troops he seems to doubt. It's the American people.

They are divided. They are angry. And al-Zawahiri is hopeful.

The negativism is feeding on itself and us. And al-Zawahiri is loving it.

No wonder that mom and dad reminded me that the biggest threat to their son isn't some other country on many days, the threat is this country.

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Neil Cavuto serves as senior vice president, anchor and managing editor for both FOX News Channel (FNC) and FOX Business Network (FBN). He is anchor of FNC's Your World with Cavuto - the number one rated cable news program for the 4 p.m. timeslot - as well as the FNC Saturday show Cavuto on Business. He also hosts Cavuto on FBN weeknights at 8 p.m. In addition to anchoring daily programs and breaking news specials on FNC and FBN, Cavuto oversees business news content for both networks and FNC's weekend business shows, including Bulls & Bears, Forbes on Fox, and Cashin' In. Click here for more on Neil Cavuto.