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In initiating a formal impeachment inquiry against President Donald Trump on Tuesday, House Speaker Nancy Pelosi did not dwell on the accusations against the chief executive. And for good reason. Additional facts are still needed about the president’s official exercise of power in asking Ukraine to investigate his political opponent, Joe Biden, as well as the former vice president’s son, Hunter Biden.

Instead, she framed Mr. Trump’s alleged behavior as a “betrayal” of three ideals rooted in the Constitution: presidential responsibility to fairly execute the law, to defend national security, and to ensure the integrity of elections. She thus offered a baseline standard, however vague or general, for judging Mr. Trump’s behavior.

Defining the good is an essential first step to any act of correction, especially in the removal of a president from office. If the House inquiry does lead to impeachment and a Senate trial, it will require broad consensus among Americans about what ideals are at stake, not just an agreement on the evidence against the president.

In today’s political climate, defining the public good is an uphill task. Ms. Pelosi did not help her cause by dropping her previous insistence that the impeachment process be bipartisan. She also might have built wider consensus by first asking the House to vote on whether to start the inquiry. Congress needs all the unity it can muster to clarify the values being used to judge the president.

The job of defining corruption or abuse of power is made easier when citizens understand the immutable principles that hold their society together and guide the behavior of public servants. The integrity of law must reflect the natural expression of higher virtues, such as equal justice, social harmony, and the dignity of each individual.

The quality of the coming debate over impeachment depends on the qualities of thought that Americans embrace for themselves and their government. Ms. Pelosi has initiated both the impeachment inquiry and a call to define the ideals at stake. Americans may not be able to influence the inquiry. But they can certainly unite around the values for judging the president’s actions.