A Senate hearing on alleged retaliation against whistleblowers at a giant nuclear cleanup project is expected to go forward on Tuesday despite the absence of some potential key witnesses: the workers who were let go.

Sen. Claire McCaskill (D., Mo.), chairman of a Homeland Security subcommittee, had planned to call two such individuals, both of whom were discharged from their jobs at the Hanford nuclear cleanup site in Washington state in the past six months. The official invitation to those people never went out, though, because...