If the criterion to be president is fitness to hold the office and the power which comes with it, then a persuasive argument can be made against Donald J. Trump, his detractors insist. Even before he won the 2016 election and was sworn into office in January 2017, he boasted of abusing women. He declared that he could shoot someone on the street and his supporters would not care. So far, he has uttered at least 16,200 false or misleading statements, according to tracking data from The Washington Post.

Trump picked some of the worst people to be his closest aides, some of them now in prison or awaiting sentencing or trial. He has provided comfort to racists seeking to make the United States a whites-only nation. His administration has forcibly separated migrant children from their parents. He has issued executive orders that threaten the climate. He maligns the courts and the media which he denounces as “enemies of the state.” His policies have divided the nation and undermined the institutions on which its traditions stand.

He has fomented trouble with America’s staunchest allies. He has further destabilized the Middle East. He has become a buddy to North Korea’s dictator Kim Jong Un and boasts that he is a friend to Vladimir Putin, president of Russia, America’s archrival. He sacrifices human rights at the altar of economic expediency.

These are some of the reasons why Trump’s opponents see him as unfit for the presidency. But fitness can be subjective and unpopular policies and even character flaws do not necessarily make someone unworthy of being the president. It is another matter when presidential behavior is detrimental threatens the national interest.

Trump crossed that line when, during his campaign, he called on Russia to hack his presidential opponent Hillary Clinton’s email server. U.S. intelligence services concluded that Russia waged a cyber campaign against the election and the Justice Department appointed former FBI director Robert Muller as special counsel to investigate whether Trump or his campaign colluded with the Russians. Twenty-four months later, Robert Muller submitted his report, finding no evidence of collusion. He did report that Russia interfered in the election “in sweeping and systematic fashion” and such interference “deserves the attention of every American.”

Muller also described 10 instances of possible obstruction of justice by Trump and the report “does not conclude that the President committed a crime” but that “it also does not exonerate him.” Muller chose to defer to a long-standing Department of Justice opinion – not a law or constitutional edict — that a sitting president may not be put on trial., so any further action would have to come from Congress. Trump seized on that outcome to claim “no collusion and no obstruction.” The House of Representatives, even with a Democratic majority, declined to launch an impeachment inquiry, seemingly further strengthening that argument.

This outcome obviously further emboldened Trump, who, according to a whistleblower, withheld $400 million in military aid to Ukraine to pressure that important American ally to launch an investigation into Joe Biden, one of his political rivals, and his son Hunter. This time, the House acted, launching an impeachment inquiry which resulted in Trump’s becoming only the third president to be impeached. He is accused of abuse of power over the Ukraine incident. Also, because he blocked the release of any document and ordered witnesses under his control not to testify, he is also charged with obstruction of Congress. The proceedings have moved to the U.S. Senate, which, on Tuesday, opened a trial, as the constitution mandates, to determine whether Trump should be removed from office. Politicians and analysts have said that impeachment is a political matter, that politics, not the evidence, dictates whether a president should be forced out of office. That is how this trial will most likely play out. Even if all 47 Democratic senators, the two Independents and a handful of Republican senators vote to convict Trump, they will likely fall far short of the needed 67 votes.

Republican senators seem to be driven by the fear that, if they find him guilty, Trump would campaign against their re-election. It is not clear how that would work if he is actually removed from office but the assumption is that he would still remain popular enough to do it. Several have said that even if Trump is guilty, his pressure on Ukraine does not rise to the level requiring his removal from office. But if trying to pressure a foreign nation to interfere in American elections for partisan, personal purposes and using the power of the office to try to stymie an investigation do not warrant a president’s removal from office, what does?

It is very likely that, if he is allowed to stay in the White House, Trump would feel free to take even more egregious actions with impunity. At some point, elected officials must be guided by the oath of office which they swore; so must the senators comprising the jurors in Trump’s impeachment trial. The alternative is to risk further damage to the nation’s democratic norms — by a president who already claims to have unlimited power.