On September 11, when President Obama authorized a series of drone strikes over U.S. soil, only this much was clear: four passenger aircraft had been hijacked and were being piloted by the hijackers.

After the aircraft had each been shot down within the space of 30 minutes and 246 casualties been identified, President Obama said in an address to the nation: “No American president would want to have to make the decision I made today, but of this much we can be sure: the citizens of this country whose lives were sacrificed, did not die in vain. Thousand more lives were saved and for this we can be grateful.”

The nation could then let out a sigh of relief, realizing that an even greater catastrophe had been averted — or maybe not.

The problem is that whenever people take actions designed to change the future, they prove that the future is not inevitable.

What happens ultimately trumps what might have happened.

So on Obama’s 9/11, all we would end up being sure of was that the president had decided that it was imperative to kill 19 hijackers even if that meant 246 Americans would become collateral damage in the process.

We might never have discovered what the aims of the hijackers were and thus the threat they posed would be a matter of conjecture.

All that would be certain was that the president saw no limits whatsoever on the extent of executive power exercised in the name of national security.

In the aftermath, what would frighten Americans more? The threat from terrorism, or the powers of the president?