A whistle-blower’s complaint released Thursday and the White House reconstruction of a phone call between Mr. Trump and the Ukrainian president, Volodymyr Zelensky, confirm Mr. Trump’s abusive pressure on Ukraine and implicate Attorney General William Barr and Mr. Trump’s private lawyer, Rudy Giuliani, in the scheme. Reports that senior members of the intelligence community referred this to the Department of Justice for possible prosecution, only to have the department refuse to investigate, cement even further the need to move forward on impeachment.

The last week underscores that Mr. Trump will pull any lever available to him to unfairly and illegally influence the outcome of the next election. His Ukraine gambit might not be the last effort to pressure foreign governments to discredit Democrats. Mr. Trump has shown that few things can deter him from illegal behavior. The Mueller report only emboldened him: His call to Mr. Zelensky came the day after Mr. Mueller testified before Congress about his findings.

The president clearly believed the lack of consequences for the actions detailed in the Mueller report gave him a green light to pursue any advantage in the next election — no matter how unethical or illegal.

The question now is not if Mr. Trump should be impeached but how. The Democrats’ political model should be the opposite of what Republicans did in 1998. The impeachment of Mr. Clinton was driven entirely by political calculation and played out exactly that way. Democrats going forward need to demonstrate that this is not about politics, but about the Constitution and the presidential abuse of power.

The fact that the House speaker, Nancy Pelosi, resisted efforts to rush to impeachment gives her enormous credibility in that regard. No one can seriously compare her to Newt Gingrich in 1998. He gleefully raced to impeachment on the thinnest of pretexts in the hopes of politically hobbling a president he opposed. Ms. Pelosi initiated impeachment only after it became clear that no other option could protect the American people and the Constitution from the abuses of a lawless president.