Congresswoman Liz Cheney’s speech Wednesday certainly was a dramatic spectacle — a Republican at war with her own party having the temerity to propose its future. The venue was the presidential foundation of Ronald Reagan, the one-time Democrat who epitomized the “Eleventh Commandment” — “thou shalt not speak ill of any fellow Republican.” She appeared as part of a series named for Reagan’s famous speech, “A Time for Choosing.”

Indeed. Ms. Cheney, often movingly, marked the ideals of the modern Republican party Reagan did so much to create: Freedom, anti-communism, limited government, free markets, family. The choice she feels the party faces now is between President Trump and the Constitution. She addressed the question head on, averring: “I know at this moment we are confronting a domestic threat we have never faced before.” Said she:

“As the full picture is coming into view with the January 6th Committee, it has become clear that the efforts Donald Trump oversaw and engaged in were even more chilling and more threatening than we could have imagined. As we have shown, Donald Trump attempted to overturn the presidential election. He attempted to stay in office and to prevent the peaceful transfer of presidential power. He summoned the mob to Washington.”

We share the values in which Ms. Cheney says she believes. We acknowledge her argument. Yet we see the work of her committee as imbalanced, damaged by the exclusion of the Republican nominees for membership. As the committee has taken on the trappings of a criminal prosecution, without the due process of cross examination, its proceedings begin to resemble a live-action and real-time violation of the prohibition of attainder.

That prohibition — against Congress trying an individual — is constitutional bedrock. The violations the Committee seeks to lay to Mr. Trump do not excuse dereliction of due process. Ditto for the tactics — false charges of collusion with Russia, illegal leaks, resistance to his efforts to carry out his mandate, a wrongful special prosecution — by which the Democrats tried to destroy Mr. Trump’s first term.

Ms. Cheney offered plenty of words against those Republicans who have yet to abandon the former president. We have yet to hear her defend the Constitution when it was — and often still is — being violated by the Democrats. Despite it all, 61 percent of national Republicans believe Mr. Trump acted appropriately on January 6. In many polls, Mr. Trump is in the van for the 2024 GOP presidential nomination.

With every passing day, meantime, it seems more clear that Ms. Cheney, by necessity and choice, has thrown in her lot with the Democrats. Literally so in Wyoming, where her campaign is asking Democrats to change their party registration so they might support her reelection. We get that politics makes strange bedfellows. We, though, prefer the strategy of the Republican bench that is working the issues in the classical, substantive way.

President Trump himself, with intermittent discipline, is reacting to the work of the January 6 Committee by talking about the policy errors of the Democratic administration — the spending, the inflation, the taxes, the regulations, the $95 tank of gas, the crime, the abandonment of the southern border — that have made these times so trying for Americans of all incomes and races. No wonder the party has yet to abandon him.

It may yet. Mr. Trump has, more than any other, broken Reagan’s rule against speaking ill of fellow Republicans. Nor does the party lack alternatives, among them Ambassador Nikki Haley, Senator Cotton, Secretary Pompeo, Governors DeSantis and Youngkin, and the heroic Mike Pence. They are all at home in the Big Tent that Reagan pitched. None has any less fidelity to the Constitution than Ms. Cheney.