There's nothing like bitter experience to test glib theories. But presidents can be remarkably slow learners, such is the power of their more cherished -- and fixed -- ideas.
Following those ideas over the cliff tends to reduce politicians to explaining why their policies were really right all along, no matter how wrong they proved in practice. See Jimmy Carter -- or, for that matter, Jefferson Davis. The first, and last, president of the Confederate States of America could still fill up two unreadable volumes explaining why his constitutional theories were absolutely right -- even as he stood amid the ruins his theories had wrought.
Other leaders wake up just in time to shake off their delusions, reverse course, and avoid the worst. Consider the case of George W. Bush. It took him the longest time to see through Donald Rumsfeld's celebrated metrics as Iraq slipped into chaos and what could have been a demoralizing defeat of Vietnam Era proportions.
In the end Dubya proved educable after all, thanks to considerable prodding from a couple of U.S. senators -- John McCain and Joe Lieberman -- and reality itself. He stopped doing the same thing over and over again expecting a different result. He changed secretaries of defense, commanding generals, and the whole set of strategies and tactics the United States and NATO had been employing in Iraq.
Indeed, he changed everything about American policy there, especially the result, and managed to snatch success from the jaws of failure. And just in time, too, for at that point he was soon to leave the Oval Office to a successor who'd promised to reverse the policies that had saved the day in Iraq.
Barack Obama, too, has finally caught on, and changed course 180 degrees in this Long War against terror. By now President Obama has embraced a whole gamut of policies he used to denounce (rather eloquently, too) as Senator and Presidential Candidate Obama. He's revived military commissions, approved warrantless wiretapping (of terrorists' international calls), and is keeping the military prison at Guantanamo open after all.
As president and commander-in-chief, Mr. Obama has come to understand that some unlawful combatants are much too dangerous to turn loose on the world. Maybe that's why he's expanded his predecessor's practice of renditions -- the transfer of certain prisoners to less hospitable confines abroad.
This commander-in-chief has also adopted tactics like targeted assassinations of terrorist leaders, cross-border attacks on enemy hideouts in Pakistan, and the use of Predator drones against an elusive foe who turns out to be not so elusive after all on happy occasion.