Empirically, however, something clearly has made us safer since 2001. Successful attacks on the United States and its interests overseas have not increased, as had been widely predicted, but instead dwindled to virtually nothing.

A steady stream of terrorist attacks on America and US interests abroad were launched from the 1980s forward. A partial history:

1988: Marine Lt.-Col. William Higgins, chief of the UN Truce Force in Lebanon, murdered by Hezbollah. Pan Am flight 103 blown up, killing 270, including a number of US military personnel.

1991: American University in Beirut bombed.

1993: Pakistani terrorist kills two agents and wounds three outside CIA headquarters. World Trade Center bombed, killing six and injuring more than 1,000.

1995: Operation Bojinka, al Qaeda's plan to blow up 12 airliners over the Pacific, discovered. Five Americans killed in attack on US Army office in Saudi Arabia.

1996: Truck bomb at Khobar Towers kills 19 American servicemen and injures 240.

1997: Terrorists murder four American oil-company employees in Pakistan.

1998: US Embassy in Peru bombed. Simultaneous attacks on US embassies in Kenya and Tanzania kill more than 300 people and injure more than 5,000.

1999: Pilot of Egypt Air flight 990 crashes airplane into ocean, killing 100 Americans, while yelling "Allahu akbar!"

2000: Suicide boat explodes next to the USS Cole, killing 17 American sailors and injuring 39.

2001: Terrorists with four hijacked airplanes kill around 3,000 Americans in New York, Washington and Pennsylvania. The "shoe bomber" tries to blow up a transatlantic flight.

After 9/11, nearly everyone expected more such attacks to follow. Instead, the pace of successful attacks against the United States slowed - and decelerated further after the onset of the Iraq war. Here's the record:

2002: Diplomat Laurence Foley murdered in Jordan, in an operation directed by Abu Musab al-Zarqawi from Iraq.

2003: Suicide bombings in Saudi Arabia kill 36 Americans.

2004: No successful attacks by terrorist groups inside the United States or against American interests abroad.

2005, 2006, 2007: No successful terror attacks inside the US or against US interests abroad.

2008: So far, no successful attacks inside the US or against US interests abroad.

(The above list omits a few "lone wolves" like the DC snipers - because the issue here is organized terrorism.)

There are a number of reasons why our government's actions after 9/11 may have made us safer:

* Depriving al Qaeda of its training grounds in Afghanistan impaired the effectiveness of that organization.

* Waterboarding three top al Qaeda leaders may have given us the information we needed to head off plots and to disable three-quarters of al Qaeda's leadership.

* The National Security Agency's eavesdropping on international terrorist communications may have allowed us to penetrate cells in America and to identify terrorists overseas.

* Al Qaeda's designation of Iraq as the central front in its war against the West may have distracted terrorists from attacks on the United States.

* The gathering of al Qaeda loyalists in Iraq, where they've been decimated by US and Iraqi troops, may have crippled their ability to launch attacks elsewhere.

* Al Qaeda's brutal conduct in Iraq may have destroyed its credibility in the Islamic world.

* The Bush administration's diplomacy may have convinced other nations to take stronger actions against terrorist groups.

* Our intelligence agencies may have gotten their act together after decades of failure.

The Department of Homeland Security may not be useless, after all.

One can debate the relative importance of these and other factors. But based on the historical record, the Bush administration obviously has done something since 2001 to dramatically improve our security against terrorism. To fail to recognize this is to sow the seeds of greatly increased susceptibility to terrorist attacks in the next administration.