A House committee is planning a showdown next week with a former Internal Revenue Service official who declined to answer questions last year about agency targeting of tea-party groups. The former official, Lois Lerner, appeared at a contentious hearing House Oversight and Government Reform Committee last May, soon after news broke that the IRS had targeted grassroots conservative groups for special scrutiny as they sought tax-exempt status. At the hearing, Ms. Lerner made an opening statement asserting her innocence of any wrongdoing, then sought to invoke her Fifth Amendment right against self-incrimination. She declined to answer questions from committee members...