The argument that there’s nothing to worry about because Mr. Trump’s Ukraine scheme didn’t work in the end misses the point. If Mr. Trump is allowed to get away with this blatant attempt at subverting the will of the 2020 voters , what’s to stop him from trying again? Remember, the phone call with the Ukrainian president, which is at the heart of the impeachment inquiry, happened just one day after the special counsel Robert Mueller testified in Congress about the end of the Russia investigation. If the House of Representatives impeaches Mr. Trump and then the Senate acquits him, it’s reasonable to assume that he would take that outcome as exoneration — and as carte blanche to do whatever he wants to win in 2020.

Throughout the hearings, House Democrats have done their job as representatives of a coequal branch of government, attempting to get to the bottom of grave allegations of wrongdoing by the president. Representative Adam Schiff, the chairman of the House Intelligence Committee, has behaved with admirable focus and restraint as his Republican colleagues have acted like children, yelling at witnesses and leaving the room when they didn’t want to hear damaging testimony.

There could well be more to come, too, if the many administration officials currently refusing to appear do the right thing and show up. Many have sent out news releases disputing witness testimony. Those witnesses were willing to testify under oath, however, at risk of perjury — and as yet Mr. Trump’s defenders have not been. If they don’t have anything to hide, why not come forward and speak under oath?

Republicans complain that this is all a partisan attack, or a “hoax,” as the president calls it. There’s no question that Democrats have their own partisan interests. But that’s no excuse for the Republicans to ignore all this evidence. In conducting this inquiry, the Democrats are doing what people concerned about protecting the nation would do. It is the Republicans who are turning this process into a partisan dogfight, attacking lifelong public servants, implying they have dual loyalty and misstating testimony they heard the day before. Rather than listening to what witnesses were telling them, some of them chose to pound the table and regurgitate conspiracy theories about Ukraine that were long ago debunked by American intelligence as Russian disinformation and misdirection.

Put this in some perspective: A party that was more than happy to impeach a president for lying about a sexual affair has refused to cast even a single vote in favor of an inquiry into whether to impeach a president who, by the credible accounts of his own appointees, has undermined national security for political advantage.

For the record: This page supported the impeachment inquiry into President Bill Clinton, as it has supported this inquiry into President Trump.

This Republican display of herd instinct is part of the broader unwillingness of the party’s leaders, and their hypocritical supporters in the partisan press, to check Mr. Trump’s most disturbing tendency of all. From the beginning of his term in 2017, President Trump has asserted broad, even monarchical, powers . He can use the extraordinary force of his office to strong-arm other countries into serving as his political pawns. He can run a protection racket with military alliances and pull out of international organizations and treaties. He can profit off the presidency. The Justice Department’s guidelines bar the indictment of a sitting president.