As a liberal Democrat who twice campaigned for President Barack Obama , I am appalled that some Democratic members of Congress are planning to boycott the speech of Israeli Prime Minister Benjamin Netanyahu on March 3 to a joint session of Congress. At bottom, this controversy is not mainly about protocol and politics-it is about the constitutional system of checks and balances and the separation of powers.
Under the Constitution, the executive and legislative branches share responsibility for making and implementing important foreign-policy decisions. Congress has a critical role to play in scrutinizing the decisions of the president when these decisions involve national security, relationships with allies and the threat of nuclear proliferation.
Congress has every right to invite, even over the president's strong objection, any world leader or international expert who can assist its members in formulating appropriate responses to the current deal being considered with Iran regarding its nuclear-weapons program. Indeed, it is the responsibility of every member of Congress to listen to Prime Minister Netanyahu, who probably knows more about this issue than any world leader, because it threatens the very existence of the nation state of the Jewish people.
Congress has the right to disagree with the prime minister, but the idea that some members of Congress will not give him the courtesy of listening violates protocol and basic decency to a far greater extent than anything Mr. Netanyahu is accused of doing for having accepted an invitation from Congress.
Recall that President Obama sent British Prime Minister David Cameron to lobby Congress with phone calls last month against conditionally imposing new sanctions on Iran if the deal were to fail. What the president objects to is not that Mr. Netanyahu will speak to Congress, but the content of what he intends to say. This constitutes a direct intrusion on the power of Congress and on the constitutional separation of powers.
Not only should all members of Congress attend Mr. Netanyahu's speech, but President Obama-as a constitutional scholar-should urge members of Congress to do their constitutional duty of listening to opposing views in order to check and balance the policies of the administration.
Whether one agrees or disagrees with Speaker John Boehner 's decision to invite Mr. Netanyahu or Mr. Netanyahu's decision to accept, no legal scholar can dispute that Congress has the power to act independently of the president in matters of foreign policy. Whether any deal with Iran would technically constitute a treaty requiring Senate confirmation, it is certainly treaty-like in its impact. Moreover, the president can't implement the deal without some action or inaction by Congress.
Congress also has a role in implementing the president's promise-made on behalf of our nation as a whole-that Iran will never be allowed to develop nuclear weapons. That promise seems to be in the process of being broken, as reports in the media and Congress circulate that the deal on the table contains a sunset provision that would allow Iran to develop nuclear weapons after a certain number of years.
Once it became clear that Iran will eventually be permitted to become a nuclear-weapon power, it has already become such a power for practical purposes. The Saudis and the Arab emirates will not wait until Iran turns the last screw on its nuclear bomb. As soon as this deal is struck, with its sunset provision, these countries would begin to develop their own nuclear-weapon programs, as would other countries in the region. If Congress thinks this is a bad deal, it has the responsibility to act.
Another reason members of Congress should not boycott Mr. Netanyahu's speech is that support for Israel has always been a bipartisan issue. The decision by some members to boycott Israel's prime minister endangers this bipartisan support. This will not only hurt Israel but will also endanger support for Democrats among pro-Israel voters. I certainly would never vote for or support a member of Congress who walked out on Israel's prime minister.
One should walk out on tyrants, bigots and radical extremists, as the United States did when Iran's Mahmoud Ahmadinejad denied the Holocaust and called for Israel's destruction at the United Nations. To use such an extreme tactic against our closest ally, and the Middle East's only vibrant democracy, is not only to insult Israel's prime minister but to put Israel in a category in which it does not belong.
So let members of Congress who disagree with the prime minister's decision to accept Speaker Boehner's invitation express that disagreement privately and even publicly, but let them not walk out on a speech from which they may learn a great deal and which may help them prevent the president from making a disastrous foreign-policy mistake. Inviting a prime minister of an ally to educate Congress about a pressing foreign-policy decision is in the highest tradition of our democratic system of separation of powers and checks and balances.
Mr. Dershowitz is a professor of law emeritus at Harvard Law School and the author of "Terror Tunnels: The Case for Israel's Just War Against Hamas" (Rosetta Books, 2014).
This article was originally published in the Wall Street Journal and may be found here.