Former Trump aide George Papadopoulos’s Russia interactions—and new details of his effort to keep other campaign officials informed of them—are calling into question previous assertions by members of the administration that they were unaware of any contacts with Russia in the lead-up to the 2016 election.

A guilty plea by Mr. Papadopoulos unsealed Monday revealed that the former campaign aide was in contact with Russian officials who claimed they could provide “dirt” on then Democratic candidate Hillary Clinton in the form...