For a growing number of President Trump’s critics, there’s already ample cause to start impeachment proceedings against him.

Last month, Trump fired FBI director James B. Comey and admitted on national television that Comey’s dismissal was connected to the bureau’s investigation into whether Trump’s associates colluded with the Russians in last year’s campaign, a fiasco that resulted in the appointment of a special counsel to handle the investigation. During a closed-door meeting with Russian officials the next day, Trump reportedly told them he got rid of Comey because he was a “nut job,” and then shared highly classified information from a U.S. ally later revealed to be Israel, endangering a major intelligence-sharing relationship.

Meanwhile, revelations concerning those in Trump’s inner circle continue to raise questions about what Trump knew and when: Trump’s transition team was reportedly aware before the inauguration that former national security adviser Michael Flynn was under federal investigation, and it recently came to light that Jared Kushner, Trump’s son-in-law and White House adviser, discussed with Russian Ambassador Sergey Kislyak about possibly using Russian facilities to set up a back channel for secret communications between the Kremlin and the Trump transition team.

Against this backdrop, it’s not surprising that the call for impeachment has officially hit the floor of the House. But for members of Congress who believe Trump must go, it would be a serious mistake to join that call prematurely. Pushing too early to impeach Trump might be the surest way to keep him in office.

A few key practical considerations weigh heavily in favor of caution. Perhaps most notably, if a concerted attempt to impeach or convict Trump fails, it will be extraordinarily difficult to assemble the political will to try a second time, even if an entirely new factual basis emerges. Call it the double-jeopardy problem, special presidential edition.

Our history of impeachments, while thin, makes clear that both phases of the removal process require an enormous expenditure of time and energy — the kind that is unlikely to be readily attempted twice. It took the House Judiciary Committee almost six months to approve and refer to the full House formal articles of impeachment against President Richard Nixon after being granted the authority to investigate whether impeachment was warranted. After Andrew Johnson and Bill Clinton were successfully impeached, the Senate took two months just to acquit each of the charges.

The problems that a first failed removal attempt will create for a second attempt are worth consideration because of the nature of the alleged misconduct and conflicts that have plagued the Trump presidency. Trump’s administration has not been derailed by a one-off scandal of dubious public dimension, like an affair with a White House intern, or even multiple abuses stemming from a discrete event, such as a break-in at a rival political party’s headquarters. Trump’s short tenure has instead been marked by an unprecedented pattern of incompetence, ethical improprieties and financial conflicts, as well as pointed disregard for national security protocol and for fact-based national security assessments. And that’s before we even get to the Russia probes. All of these factors suggest impeachment might be appropriate tomorrow even if it isn’t appropriate or sufficiently popular to garner the consensus necessary for Trump’s ouster today.

Commentators like to point out that during the Constitution’s drafting, James Madison emphasized that an impeachment clause was “indispensable” to safeguard the community against “the incapacity, negligence or perfidy of the chief Magistrate.” In other words, the availability of the option is important to the well-being and security of our country. That means taking a protective rather than promiscuous approach to impeachment, with an understanding that it is a defensive weapon whose use can, as a political matter, probably be attempted only once.

Patience is all the more crucial given the tremendous uncertainty created by the ongoing Justice Department and congressional investigations into possible collusion between the Trump team and Russia. Last month, Rep. Adam B. Schiff (Calif.), the ranking Democrat of the House Intelligence Committee, rightly cautioned against rushing to action “without understanding the full evidence of what the president may or may not have done.” This is true in a general sense; an incomplete picture is always a problematic basis for a measure as drastic as impeachment, whether the public official is a federal judge or the president of the United States.

But Schiff’s warning is also a helpful reminder that the various open Russia investigations serve as a kind of wild card in the public imagination. Because questions about the Trump campaign’s contacts with Russia remain unresolved, impeachment for any related alleged misconduct will be widely seen as premature. That perception, in turn, will undermine the consensus required for successful removal. The House needs only a simple majority to impeach the president for “Treason, Bribery, or other high Crimes and Misdemeanors.” But two-thirds of the Senate must vote to convict. This is not just an extremely high bar — it’s a bar that has never been cleared in our history.

Some have argued that we are in impeachment territory irrespective of the findings of those investigations, based on what we already know of Trump’s statements and actions. Most prominently, constitutional scholar Laurence Tribe argues that, by Trump’s own admission, his firing of Comey was motivated by the FBI’s Russia probe and therefore constitutes clear obstruction of justice. But the political reality is that the perceived legitimacy of impeaching Trump for obstruction of the FBI’s Russia investigation will turn in great part on how that investigation itself shakes out. If you doubt this, imagine for a moment that Trump is impeached and convicted of obstruction of justice for firing Comey or similar conduct, and that he and his team are subsequently cleared of any criminal wrongdoing regarding Russia’s interference in the election. No result could better support Trump’s claim that the Russia investigation was, all along, a baseless “witch hunt” designed to bring him down.

Under any administration, impeachment must be broached with great reluctance. As the late Yale Law professor Charles Black explained in his famous little handbook on impeachment, first published during the Watergate crisis, “[t]he presidency is a prime symbol of our national unity.” Given “the deep wounding such a step must inflict on the country,” Black argued that we must resort to dismantling the presidency “only when the rightness of diagnosis and treatment is sure.”

But in these abnormal times, Black’s plea for nonpartisan sure-footedness is all the more compelling. Where its rightness is unsure, an impeachment effort risks our national unity. Where its results are uncertain, such an effort could take a viable tool off the table for future crises and risk our national security as well.