When Prime Minister Netanyahu goes before the joint meeting of Congress on Tuesday, he will be stepping onto some of the most treacherous territory in the whole Middle East debate. We speak not of the contested acres between Israel and the Arabs but rather the territory between the Congress and the presidency and the battle between the two for supremacy in foreign affairs.

It’s one thing for the prime minister of Israel to disagree with the president of America. It happens all the time, and we don’t mind saying that sometimes it is the president of America who is in the wrong, as we believe Mr. Obama is in respect of the 1967 borders. It’s another thing, however, for the prime minister of even a friendly country to go over the head of the president directly to the Congress.

Not that it doesn’t happen. Mr. Netanyahu himself addressed a joint meeting of the Congress in 1996. He was a newly installed prime minister and free market reformer from a country that had long suffered from socialist economic policies, as the editor of the Sun put it in a piece a year ago in the Wall Street Journal. The Israeli was speaking to a Congress in which another free-market reformer, Newt Gingrich, had recently acceded to speaker. That was the occasion on which Mr. Netanyahu declared that there would “never” be a division of Jerusalem again. “Never.”

When he repeated the word “never,” the whole Congress rose in a standing ovation. It was one of the most memorable and visible demonstrations in the whole history of Israeli-American relations of the grass roots support that the Jewish state enjoys in the American democracy. One could call it a kind of demonstration by the Israeli leader that he had other places than the White House to go for support in the difficult challenges that Israel was then facing. The demarche was said to have infuriated the president at the time, William Clinton.

Mr. Clinton, however, had openly intervened against Mr. Netanyahu and his Likud Party in the election in Israel that had just sidelined the dovish Labor party leader, Shimon Peres, who was much more to Mr. Clinton’s liking. Messrs. Clinton and Netanyahu joked about it in a press conference shortly before Mr. Netanyahu went up the hill to speak to the Congress. “Sometimes I wish I could explain things that don’t need much explaining,” a rueful Mr. Clinton said, according to Steven Erlanger’s dispatch in the Times.

The big question in the current crisis is whether Congress is eventually going to assert itself against the pro-Palestinian tilt that the administration has taken and, if it does, whether the Congress itself will win the day. The Congress has tried to assert itself on a number of occasions, particularly over Jerusalem. The Congress wants the American embassy in Tel Aviv moved to Jerusalem, which is the capital of the Jewish state and was annexed following the Six-Day war in 1967. But the Congress has been rebuffed by successive presidents, Democrats and Republicans.

It happens that the Supreme Court has just agreed to hear a lawsuit, in which a nine-year-old boy, Menachem Binyamin Zivotofsky, is asking for enforcement of another law in which the Congress has tried to assert itself in respect of Jerusalem. The Congress had passed the measure in 2002, saying that, if requested to do so, the state departement had to issue to Americans born in Jerusalem a certificate listing their birthplace as Israel. The law passed Congress by an over-whelming bi-partisan margin, but two presidents, Messrs. Bush and Obama, have refused to enforce it, on the theory that it infringes on the constitutional prerogatives of the president in foreign affairs.

The nine-year-old boy who brought the suit the Supreme Court has agreed to hear was born at Jerusalem in 2002. The boy’s attorney, Nathan Lewin, has suggested that no great foreign policy issue is at stake. But the Supreme Court itself has asked the lawyers to brief the justices on whether the law “impermissibly infringes the President ’s power to recognize foreign sovereigns.” It’s shaping up as a rare test of how much authority the Congress has, under the Constitution, in foreign affairs.

In recent decades the conservatives have been with the president in this contest, particularly during the Reagan years when the Congress was trying — unconstitutionally, conservatives suggested — to limit the president’s war powers. This was particularly true in the wake of Vietnam, when the Congress used a war powers act it had concocted to try to cramp President Reagan’s ability to maneuver against the Marxist Sandinista regime in Nicaragua. Now the shoe is on the other foot, and a Democratic president is maneuvering in the face of a more conservative Congress, including this week over his authority to act without a vote of Congress in Libya.

Was it wise for Mr. Netanyahu to take his case to Capitol Hill? One doesn’t get to address a joint meeting of Congress without being invited, and no doubt he will get a rousing and warm welcome. But it’s a moment to remember that the territory is treacherous. For Congress can be as fickle as the presidents have been. It was on Capitol Hill that the cause of a free Vietnam was lost in 1975. And it doesn’t bode well that for all the applause the Congress gave Mr. Netanyahu 15 years ago, the solons have left the heavy constitutional lifting on the bedrock question of Jerusalem to a 9-year-old boy.