The whistleblower complaint that has triggered a tense showdown between the U.S. intelligence community and Congress involves President Trump’s communications with a foreign leader, according to two former U.S. officials familiar with the matter. Trump’s interaction with the foreign leader included a “promise” that was regarded as so troubling that it prompted an official in the U.S. intelligence community to file a formal whistleblower complaint with the inspector general for the intelligence community, said the former officials, speaking on the condition of anonymity because they were not authorized to discuss the matter publicly. It was not immediately clear which foreign...