The Washington Post reports: As a junior senator with presidential aspirations, Barack Obama built his persona in large part around opposition to Bush administration counterterrorism policies, and he sponsored a bill in 2005 that would have sharply limited the government’s ability to spy on U.S. citizens.

That younger Obama bears little resemblance to the commander in chief who stood on a stage here Friday, justifying broad programs targeting phone records and Internet activities as vital tools to prevent terrorist attacks and protect innocent Americans.

The former constitutional law professor — who rose to prominence in part by attacking what he called the government’s post-Sept. 11 encroachment on civil liberties — has undergone a philosophical evolution, arriving at what he now considers the right balance between national security prerogatives and personal privacy.

“I came in with a healthy skepticism about these programs,” Obama said in San Jose on Friday. “My team evaluated them. We scrubbed them thoroughly. We actually expanded some of the oversight, increased some of safeguards. But my assessment and my team’s assessment was that they help us prevent terrorist attacks.”

“On net,” the president added, “it was worth us doing.”

As Obama strived to reassure the American people following startling revelations this week about top-secret federal data-mining and surveillance programs, he said that he, too, has long been torn on the issue and that there is no easy answer.

“You can’t have 100 percent security and also then have 100 percent privacy and zero inconvenience,” he said. “We’re going to have to make some choices as a society.”

But are Americans in large numbers or any numbers calling for or expecting 100 percent security? An expectation of perfect security is no more realistic than the expectation that citizens will have perfect trust in their government and the absence of a basis for such perfect trust is exactly why the powers of government must always be constrained.