On Wednesday, Donald Trump became the third president in American history to be impeached by the House of Representatives. The articles of impeachment stretch across nine pages. But the most important clause is on page five, in the second paragraph: “President Trump, by such conduct, has demonstrated that he will remain a threat to national security and the Constitution if allowed to remain in office,” it reads.

This is the core of the case against Trump and why the Senate cannot shirk its duty. The first years of Trump’s term were marked by an investigation into whether Trump colluded with Russia to warp the 2016 election. The president repeatedly and angrily denied the allegations, and in the end, special counsel Robert Mueller’s investigation did not find proof of direct coordination between Trump and Russian President Vladimir Putin, though it did find repeated efforts on Trump’s behalf to obstruct the investigation.

In the aftermath of that investigation, Trump turned to Ukraine and did exactly what he was accused of doing with Russia. He sought to collude — or, more accurately, extort — a foreign government into helping him win a domestic election. The facts of this aren’t in doubt and haven’t been since September, when Trump released an edited record of his “perfect” conversation with Ukrainian President Volodymyr Zelensky.

If Trump’s behavior is exposed but the Republican Party protects him from consequences, the lesson he’ll draw is clear: Do it again, but more so. That’s the pattern connecting his behavior from the Russia affair to the Ukraine breach.

It’s the pattern of Trump’s career more broadly: If something works for him, he does it again — and he does it bigger, louder, and more aggressively. You can see it in Trump’s escalation from birtherism to calling Mexicans rapists and murderers, you can see it in how he went from putting his name on his own towers to putting it on anything that would cut him a check, you can see it in how he realized he could refuse to pay contractors and turned it into a business practice.

Perhaps this might be different if Trump had admitted his error and apologized after the Ukraine scandal was revealed. But he has done the opposite. In the bizarre letter Trump sent to House Speaker Nancy Pelosi on the eve of the impeachment vote, he wrote, “Every time I talk with a foreign leader, I put America’s interests first, just as I did with President Zelensky.”

In this, I take Trump at his word. It’s classic authoritarian-populist psychology to conflate the personal interests of the leader with the interests of the country. But this is precisely what makes it so dangerous for Trump to emerge unscathed and emboldened: Trump believes what he did was right, and that the wrongdoing is entirely on the part of the Democrats and the media, who are unfairly persecuting him. So why wouldn’t he do this, and worse, again — particularly as the 2020 election nears and his legacy hangs in the balance?

This is why the framers added the impeachment power

Harvard Law School professor Noah Feldman was one of four constitutional law experts asked to testify before the House Judiciary Committee on impeachment. There are questions of constitutional intent and interpretation that are genuinely hard, Feldman told me. But not this one. “This is just one of those cases where it’s just not that complicated,” he said.

“The framers had this one conversation on July 20, 1787, where they laid out in really clear terms what they were worried about,” Feldman continued. “They worried about the abuse of power by a president for his personal gain, to corrupt the electoral process and to subvert national security. That’s it. That’s why they put impeachment in there.”

Republicans do not want to impeach a Republican president. That was evident in the House vote, in which every House Republican voted against impeachment, and it’s been evident in the comments by Senate Republicans preparing for the coming impeachment trial.

“Everything I do during this, I’m coordinating with the White House counsel,” Senate Majority Leader Mitch McConnell assured Sean Hannity on Fox News. “There will be no difference between the president’s position and our position as to how to handle this.”

Sen. Lindsey Graham, the South Carolina Republican who exchanged a reputation for moderation for a reputation for Trumpist sycophancy, was even crisper. “This thing will come to the Senate, and it will die quickly, and I will do everything I can to make it die quickly,” he said.

The question animating Richard Nixon’s impeachment was, famously: What did the president know, and when did he know it? But that has never been the question with Trump. Since the release of the White House call record, it’s been clear that he knew everything, because he was the one directly making the ask of President Zelensky.

No, the question at the heart of Trump’s impeachment has been: What will the Republican Party accept, and even defend? And the answer, so far, is everything Trump did and more.

In our conversation, Feldman made a point that has rang in my head, uncomfortably, ever since. It would almost be better, he told me, if Republicans simply said Trump’s actions were wrong but that the power of impeachment was too divisive, and too severe, to deploy. But the argument they’re actually converging around — in part because it is the argument Trump himself makes — is that there was nothing improper in what Trump did.

“That, to me, is genuinely dangerous because then they’re defining deviancy down,” said Feldman. “They’re defining an impeachable offense to exclude conduct that is profoundly dangerous to the union, to national security, and to the nature of democracy. They’re saying to Donald Trump, go ahead and do it in the future, and that’s bad enough. But they’re also saying it to every future president. Go ahead and use the office of the presidency to gain personal political advantage in upcoming elections. And that’s genuinely destructive.”

This is why the most important part of the articles of impeachment are those 25 words on page five. Impeachment’s most important role is preventive, not retributive. It is to make sure that neither Trump nor any future president tries to abuse their power to amass more power in this way again. But if Senate Republicans abdicate their constitutional duty and, as Graham promised, do everything they can to make this die quickly, they’ll be unleashing Trump and his successors to abuse the power of the presidency even more flagrantly in the future.