Sen. Ron Johnson (R-WI) has conducted transcribed interviews with “more than half a dozen” former Biden officials as part of his investigation into the ex-president’s apparent mental decline.

In a brief interview, Johnson, who runs the investigative arm of the Senate’s Government Affairs Committee, declined to name the officials who sat for interviews but previously disclosed that Tom Vilsack, the former agriculture secretary under President Joe Biden, was the first to appear earlier this summer.