The vote in the Senate yesterday to defy President Obama’s threat to veto legislation that would give the military the first chance to interrogate operatives of al Qaeda, even those who are American citizens captured here at home, sets up a situation to watch. The president is determined to preserve his constitutional authority over the military. The congress, however, is hell bent on ensuring that, as it was put by a leading senator from Mr. Obama’s Democratic Party quoted in the Washington Times, “people determined to be part of al Qaeda should be treated as people who are at war with us.”

We’re not terribly concerned one way or another on the merits of the legislation, though our instinct is that we’re inclined to agree with the president. What does interest us is the growing tension between the Congress and the President over war powers and foreign policy. There was a time when we would reflexively side with the president in that test of wills, an instinct awakened during the struggle over whether to sever American support for Free Vietnam as it was facing a communist onslaught. Our instinct was also tested during the war of the Contras in central America.

A long newspaper life, however, has taught us not to sell the Congress short. It may have been wrong about Vietnam but it was, in the end, dispositive. We’ve come to the view that even when the president is in the right, he is courting trouble to simply waive off the Congress. Often in recent years, moreover, Congress has often been wiser than the president. The Supreme Court is now weighing the refusal of President Obama to enforce a law passed by Congress requiring the state department to issue, when asked to do so by an American born at Jerusalem, a passport listing the country of birth as Israel.

So what is Mr. Obama going to do about the interrogation legislation moving through the Senate? He could simply veto the bill and hope the Congress, in which the Senate is controlled by his own party, fails to override. If it does over-rides a veto, and the measure becomes law, he could ignore it and take his chances in court, or in an impeachment. Or he could sign the legislation when it passes and issue a signing statement saying he won’t enforce it. That is what happened when President Bush was presented with a law relating to Americans born in Jerusalem.

Congress passed the law, requiring the state department to issue a passport listing Israel as the country of birth to any American born in Jerusalem who asks for such a passport. Mr. Bush signed the measure, which was part of a larger bill, but said the Jerusalem passport section was an unconstitutional infringement on his authority to receive foreign ambassadors and, thus, conduct relations with foreign states. An American born at Jerusalem promptly sued, and the Supreme Court is now weighing the question.

What strikes us as noteworthy about the current contretemps is that we’re in a patch in which the Congress is more aggressive about asserting America’s position than the executive. During the Reagan era it was the other way around. Now the president seeks, in effect, to veto part, but not all, of the bills he either signed or may soon be presented for signing. It’s kind of like the line-item veto fight, which was finally ended by the Supreme Court when, in 1998, it ruled against such partial vetoes in a case called Clinton v. City of New York — a case in which it became harder than ever for a president to take Congress for granted.