As subsequent reporting has revealed, among the whistle-blower’s core allegations is that Mr. Trump pressured a foreign government to take steps that would damage a political rival, former Vice President Joe Biden, the front-runner for the Democratic presidential nomination. In a July phone call with the newly elected president of Ukraine, Volodymyr Zelensky, Mr. Trump is said to have repeatedly urged Mr. Zelensky to work with Rudy Giuliani, the president’s personal lawyer, on a corruption investigation of Mr. Biden, focused on the tenure of Mr. Biden’s son Hunter on the board of a Ukranian gas company.

At issue is not whether Mr. Trump spoke to his Ukrainian counterpart about Mr. Biden or even whether he accused Mr. Biden of corruption. The president acknowledged as much on Sunday, when he told reporters, “The conversation I had was largely congratulatory, with largely corruption, all of the corruption taking place and largely the fact that we don’t want our people like Vice President Biden and his son creating to the corruption already in the Ukraine.”

This jibes with what Mr. Giuliani said — far more combatively — in a Thursday interview on CNN. Pressed on whether he had asked Ukrainian officials to look into Mr. Biden, Mr. Giuliani initially said no, then, upon further questioning, declared, “Of course I did!”

Whatever the nature and impetus for Mr. Trump and Mr. Giuliani’s pressure campaign, it came at a delicate moment in relations between the United States and Ukraine, a former Soviet republic. This summer the Trump administration, without any warning, temporarily held up $250 million in military aid aimed at helping Ukraine defend itself against aggression by Russia. At the time, the administration said it was reviewing the program to make sure the money was being used in the best interest of the United States. The money was released this month, the same week that three House committees announced plans to look into whether Mr. Trump had pressured Ukraine to investigate his political rival and whether his administration had suggested, explicitly or implicitly, that the aid money was contingent on that help.

This is a complicated situation, and there are serious questions begging to be cleared up. The White House has worked to prevent that from happening. By refusing to turn over the whistle-blower report, the administration is following the same playbook it has used for all of Congress’s inquiries: deny, deflect and delay — possibly indefinitely.