The White House has said Mr. Trump fired Mr. Linick at the urging of Secretary of State Mike Pompeo, and Democrats have opened an investigation. Mr. Biden spoke in forceful terms about his disappointment in some of his former Republican colleagues.

“That used to be a hobbyhorse for Republican senators,” said Mr. Biden, the presumptive Democratic presidential nominee and previously a longtime Delaware senator. “Republican senators joined Democrats, they were strongly, strongly, strongly supportive of these independent inspector generals.”

That applied to Republicans “starting with” Senator Charles E. Grassley of Iowa, Mr. Biden said.

“Where are they?” he continued. “Why aren’t they speaking up about this? It really bothers me. It bothers me a lot.”