It was a sadly ironic image broadcast from John Brennan's Senate Intelligence Committee confirmation hearing last week: a handful of protestors being herded out by police.

Not so long ago, those women denouncing targeted drone killings and shouting they were there to represent the mothers of Pakistan and Afghanistan might have been the ones cheering, "Yes we can!" in support of candidate Barack Obama. Now, the president who won election pledging a new kind of global engagement is claiming the right to selectively kill Americans abroad who are only suspected of terrorism.

Obama supporters who criticized President George W. Bush for just that sort of indifference to constitutional principles are being excoriated by conservative opinion-shapers like Cal Thomas and The Wall Street Journal editorial page. And rightly so, if we remain silent on a stance that doesn't square with the principles that got Obama elected.

It's not a good sign when the White House resists even releasing its legal basis for targeting and killing U.S. citizens. House and Senate intelligence committee members got to see the papers on the eve of Brennan's hearing after being "stonewalled," as Sen. Ron Wyden, an Oregon Democrat, put it.

Obama has relied on the use of unmanned drones to kill suspected terrorists around the world. Brennan, Obama's nominee for CIA director, was his top counter-terrorism adviser, and testified the policy on killing Americans is to strike only to save lives when an attack is imminent and there is no alternative. But the Justice memo provides a lot more latitude.

In accepting the Nobel Peace Prize in 2009, Obama said, "I believe the United States of America must remain a standard bearer in the conduct of war. That is what makes us different from those whom we fight. That is a source of our strength." He went on to say, "That is why I prohibited torture. That is why I ordered the prison at Guantanamo Bay closed." Of course, the notorious abuse-riddled detention facility he once called a recruiting ground for terrorists remains open despite an executive order by Obama to close it.

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As a presidential candidate, he pledged to stop using military tribunals in the war on terror, saying the criminal justice system and courts-martial were appropriate. Then in 2010, Omar Khadr, the Canadian son of an al-Qaida leader, was tried before one for murder. He confessed to throwing a grenade at age 15 that killed a U.S. solider in Afghanistan. International conventions call for children accused of war crimes to be tried according to juvenile justice standards. The press was barred from even covering his trial.

Obama once decried the indefinite detention of suspects, but he has allowed some to be indefinitely detained. His administration has said there is no role for the courts in this, and Brennan expressed skepticism about getting prior judicial approval.

The White House has resisted lawsuits by the family of Anwar al-Awlaki, who was killed with his teenage son and another man, all Americans, in 2011 drone strikes in Yemen.

But some lawmakers, including Sen. Angus King, an independent from Maine, have proposed a special federal "drone court" that would approve who should be targeted, and the White House is said to be considering one. Implementing one would be the very least it could do.

Democratic Sen. Dick Durbin of Illinois, appearing on "Meet the Press" last Sunday, called the war on terror a "different kind of war," and said there would be congressional hearings on how to square it with the constitution.

But we've seen from the previous administration how merely changing the terminology enables the administration to change accepted international rules of war conduct. That's not good enough.

Here are some uncomfortable questions a congressional hearing could consider: Could there be a situation in which the president ordered a targeted drone killing on U.S. soil of an American suspected of, say, mass murder? And how do we respond to other countries deciding to use drone strikes over American territory?

No matter how loyal one may feel to an eminently likeable and in many ways outstanding president, no leader is entitled to unconditional support for policies that raise such constitutional questions and defy such core American values as this one does.

Rekha Basu is a Des Moines Register columnist.