Impeachment of a president, whether it results in removal from office or not, is a serious matter. House Democrats have taken the first step on that road, opening an inquiry that could build a case for articles of impeachment.

That they waited nearly a year after taking the majority to do so speaks to the fact that this is no rush to judgment. But after reports that President Donald Trump had attempted to enlist a foreign government in investigating a chief political rival in the upcoming election, Democrats had little choice.

Since taking office, Trump has upended many conventional norms. But the efforts to get the Ukrainian government to investigate former Vice President Joe Biden, a leading contender for the Democratic nomination, go too far. Americans already know that Russia interfered in the 2016 election, attempting to tip the scales to Trump. A lengthy investigation proved that, although it did not prove that candidate Trump conspired in the meddling.

This time, we have the president’s own words, in a five-page memo summarizing a half-hour phone call to Ukrainian President Volodymyr Zelensky, in which Trump repeatedly reminds Zelensky how much the U.S. has done for his country. Zelensky knew that just days earlier, Trump had inexplicably frozen $400 million appropriated by Congress as aid to Ukraine. Then he hears the president make this startling request: “I want you to do us a favor.” What follows crosses every ethical boundary an American president should have.

Trump not only implores Zelensky to investigate Biden, he asks him to work with Rudy Giuliani, Trump’s personal attorney, who holds no position in the government. And with U.S. Attorney General William Barr. That elevates the request to one that carries the full weight of the federal government.

Impeachment is so serious an action that Congress must undertake a thorough investigation, as is happening now. The issues at hand go beyond a single phone call. Giuliani has already said that his efforts in Ukraine to investigate Biden came at the behest of the State Department. “I never talked to a Ukrainian official before the State Department called and asked me to do it,” Giuliani said during an appearance on Fox News. And although it runs five pages, the declassified memo — which is not a verbatim transcript — contains several ellipses, indicating missing passages.

The investigation must be thorough because if it comes to a vote on articles of impeachment, the American public must have a complete accounting of the facts. There can be no room for credible accusations that Democrats are merely engaged in a hasty witch hunt. Democrats should establish clear boundaries, a timeline and be as transparent as possible if they want to restore a measure of trust with their actions.

An impeachment battle could deepen divisions in an already polarized country. But there are other risks as well. There is the risk to election integrity if we do nothing, and let yet another standard fall. Americans must be convinced that the integrity of the upcoming election will not be tainted by the actions of yet another foreign government. And the office of the presidency, so central to American leadership in the world, must be protected.

The nation would be better served by bipartisan support for the inquiry. But at least for now, Republicans appear fixated on what they consider the lack of a quid pro quo. But as the House committee chairs countered in a joint statement, “No quid pro quo is required to betray our country. Trump asked a foreign government to interfere in our elections — that is betrayal enough.”

An inquiry by itself is not impeachment. It is a search for the truth. And it is desperately needed.