When Jared Kushner, President Trump’s son-in-law and senior adviser, sought the top-secret security clearance that would give him access to some of the nation’s most closely guarded secrets, he was required to disclose all encounters with foreign government officials over the last seven years.

But Mr. Kushner did not mention dozens of contacts with foreign leaders or officials in recent months. They include a December meeting with the Russian ambassador, Sergey I. Kislyak, and one with the head of a Russian state-owned bank, Vnesheconombank, arranged at Mr. Kislyak’s behest.