President Trump returned home on Saturday to confront a growing political and legal threat, as his top aides tried to contain the fallout from reports that his son-in-law, Jared Kushner, is a focus of investigations into possible collusion between Russia and the president’s campaign and transition teams.

As Mr. Trump ended a nine-day overseas trip that aides considered the most successful stretch of his presidency, he was returning to a crisis that had only grown in his absence. The White House canceled a presidential trip to Iowa in the coming days and was putting together a damage-control plan to expand the president’s legal team, reorganize his communications staff and wall off a scandal that has jeopardized his agenda and now threatens to engulf his family.

Mr. Trump’s private legal team, led by his New York lawyer, Marc E. Kasowitz, was preparing to meet in Washington to face new questions about contacts between Mr. Kushner and representatives of President Vladimir V. Putin of Russia. Mr. Trump may meet with Mr. Kasowitz as early as Sunday, and aides have recruited a series of prominent Washington lawyers with experience in political investigations for Mr. Trump to interview in hopes that they might join the legal team.

Mr. Kushner, who organized the president’s Middle East stops at the start of the foreign trip, chose to return to Washington with several days to go and has been unusually subdued since then. But he has no plans to step down from his role as senior adviser or to reduce his duties, according to people close to him.