At 6:14 p.m. on June 7, 2016, Donald Trump Jr. clicked the send button on an email to confirm a meeting with a woman described as a “Russian government attorney” who would give him “information that would incriminate Hillary and her dealings with Russia.”

Three hours later, his father, Donald J. Trump, claimed victory in the final primary races propelling him to the Republican presidential nomination and a general election contest against former Secretary of State Hillary Clinton. In his victory speech, Mr. Trump promised to deliver a major address detailing Mrs. Clinton’s “corrupt dealings” to give “favorable treatment” to foreign governments, including “the Russians.”

The White House said the timing was a coincidence. The younger Mr. Trump said this week that he never told his father about the meeting with the Russian lawyer, and the president said on Wednesday that he did not know about it until a few days ago. But the time frame raised questions that investigators will presumably examine as they try to piece together who knew what, and when, last year during what American intelligence agencies have called a Russian effort to influence the presidential election.