Whatever one may think of President Trump's speech last Wednesday—I personally found it deeply upsetting—one thing is clear: It was fully protected by the First Amendment. Nothing the president said constituted unprotected "incitement," as narrowly defined by the Supreme Court over nearly a century of decisions. His volatile words plainly fell on the side of political "advocacy," which is protected speech.

In the leading case of Brandenburg v. Ohio, a unanimous Supreme Court ruled that even the advocacy of the use of force is constitutionally protected, unless it is specifically "directed to inciting or producing imminent lawless action." In subsequent decisions the courts have narrowly defined "incitement" to exclude the kind of speech delivered by President Trump. It is beyond dispute, therefore, that his speech—disturbing as it may have been—is within the core protection of political speech.

If that is correct, then the following question arises: whether the constitutional criteria for impeachment—"treason, bribery or other high crimes and misdemeanors"—can plausibly be understood to encompass constitutionally protected expression; that is, speech that could not constitutionally be made criminal under the First Amendment's mandate that "Congress shall make no law ... abridging the freedom of speech." The constitutionally correct answer to that question is surely no.

So the article of impeachment Democrats introduced in Congress—which focuses on President Trump's speech that urged listeners to go to the Capitol—is unconstitutional. Impeaching President Trump on grounds that violate both the First Amendment and the impeachment clause would do more serious and enduring harm to our Constitution than the unlawful rioters did when they temporarily took over the Capitol building. These rioters did grave harm to the rule of law, but at the end of a long and difficult day, the rule of law prevailed. The Capitol was secured and Congress continued with its business, voting down what the rioters were demanding. Many of those who broke the law have been arrested and will be prosecuted and convicted for serious crimes including possibly homicide. But now, the Democratic leaders of Congress and some Republicans are threatening to take political steps that endanger the line carefully drawn by First Amendment jurisprudence between those who advocate unlawful conduct and those who commit it.

When the Supreme Court notoriously upheld the unconstitutional detention of more than 100,000 Americans of Japanese descent during World War Two, Justice Robert Jackson issued a memorable dissent that is relevant to our current situation. He acknowledged that the military order in question was "not apt to last longer than the military emergency." But Jackson argued that when it is "rationaliz[ed] to show that the Constitution sanctions such an order," the precedent "lies about like a loaded weapon ready for the hand of any authority that can bring forward a plausible claim of urgent need." The same would be true of an impeachment based on a constitutionally protected speech that caused several hours of inexcusable violence.

People gather at the base of the U.S. Capitol with large IMPEACH and REMOVE letters on January 12, 2021 in Washington, DC.Paul Morigi

Defending the First Amendment does not require agreement with what the president said. I strongly disapprove of much of the content of his speech and wish he hadn't given it, but I stand with the defense of free speech attributed to Voltaire more than 200 years ago: "I disapprove of what you say, but I will defend to the death your right to say it."

Thomas Jefferson, in a letter written 25 years after the signing of the Declaration of Independence, strongly opposed the prosecution of speakers who advocate unlawful conduct, arguing that the "safer corrective" is for the law to stand "ready to punish the first criminal act produced by the false reasoning" of the speaker.

The major criterion for this impeachment—"incitement to sedition"—has been misused throughout our history in efforts to suppress the advocacy of controversial speakers, including union leaders, civil rights activists, suffragettes and other protesters and dissenters. It is an open-ended concept that can be expanded to cover many constitutionally protected protests. That is why the Supreme Court has repeatedly rejected efforts to circumvent the First Amendment by accusing advocates of "incitement," "sedition," "insurrection," "treason" and other loaded but vague phrases and words. Even when a speaker's advocacy is the "but for" cause of the resulting violence—as it was on Wednesday—the First Amendment protects it unless the speaker expressly incited the violence that immediately ensued. That is not what President Trump did.

Those who would compromise our hard-earned constitutional rights for short-term partisan expediency are ignoring the big picture. Weaponizing the Constitution as a political sword has consequences. Today it is being wielded against a Republican president. Tomorrow it may be wielded against a Democratic president. As Senator James N. Grimes warned during the impeachment trial of President Andrew Johnson, removing a president on grounds not specified in the Constitution would normalize "impeachment as part of future political machinery." That is what has been happening since the Republicans improperly impeached President Bill Clinton in 1998.

Even if those seeking to end President Trump's term by unconstitutional means are well intentioned, they must not be allowed to damage our Constitution. As Justice Louis Brandeis cautioned a century ago: "The greatest dangers to liberty lurk in insidious encroachment by men [and women] of zeal, well meaning but without understanding."

President Trump has now called for an orderly transition of power. Democrats should not interfere with this transition by demanding a divisive two-step transfer—first to Vice President Pence for a few days and then to president-elect Biden—by means of an unconstitutional impeachment.

Follow Alan Dershowitz on Twitter @AlanDersh and on Facebook @AlanMDershowitz. His new podcast, The Dershow, can be found on Spotify, YouTube and iTunes.

The views expressed in this article are the writer's own.