This time, Mr. McConnell is disinclined to have any witnesses testify at all. His goal is to keep the trial as perfunctory as possible, based on the president’s and the Republicans’ insistence that the process has been illegitimate and should be dispatched as quickly as possible. He has suggested that he will ram through the rules on a partisan vote if he and the Senate’s Democratic leader, Chuck Schumer, do not reach an agreement.

Even the president’s legal team has expressed concerns about Mr. McConnell’s approach. The White House counsel, Pat Cipollone, has observed that, by refusing to conduct a proper trial, Mr. McConnell removes the possibility of additional information being presented that could exonerate Mr. Trump. But due process and exoneration are not the majority leader’s concern. A swift acquittal is.

In an open letter to Mr. McConnell on Sunday, Mr. Schumer called for a more serious trial, complete with crucial witnesses and additional documents that, thus far, the White House has refused to provide. Mr. McConnell promptly attacked Mr. Schumer for airing his request publicly in advance of their private negotiations.

It is a central puzzle of the impeachment process so far: If, as the president claims, he did not try to withhold congressionally mandated aid to force Ukraine to meddle in the 2020 election, why won’t he allow any senior administration officials to testify about his actions and clear him? This puzzle only grows more vexing as the case nears the Senate, where Republican control could surely provide Mr. Trump the fair hearing he insisted the House wouldn’t give him.

Democratic leaders are right to shine a spotlight on how the trial will be conducted. The only hope of achieving a thorough (or at least less phony) process is for public pressure to be applied — not on Mr. McConnell, but on members of his conference not yet ready to be written off as presidential puppets.

With the rules governing an impeachment trial set by a simple majority, only four Republicans need to stand up to Mr. McConnell and demand better, if not out of courage then out of the fear of the political costs of going along with his sham proceeding. (As few as three Republicans could do the trick with the help of Chief Justice John Roberts, who will preside at the trial and must break any tie.) Senators facing tough re-election races next year — including Susan Collins, Martha McSally, Cory Gardner and Thom Tillis — might well have an interest in projecting independence and integrity.

To be sure, in withholding the articles from the Senate, Ms. Pelosi is attempting a tricky balancing act. The longer she delays, the more likely it is that Republicans will be able to paint her as playing political games. Already, Mr. McConnell has suggested that the delay stems from her embarrassment over the House’s “shoddy work product.”