FROM THE WALL STREET JOURNAL—A House committee chairman called on President Barack Obama to fire the Internal Revenue Service commissioner, John Koskinen, over his handling of congressional probes into alleged targeting of conservative groups by the agency. In a letter, Rep. Jason Chaffetz (R., Utah) accused Mr. Koskinen of “obstruction” of congressional investigations. In a statement, Mr. Chaffetz, chairman of the House Oversight and Government Reform Committee, also vowed to pursue other remedies, “including potential contempt proceedings or perhaps impeachment of Commissioner Koskinen.” The demand follows a series of potentially embarrassing developments for the agency in its responses to congressional inquiries. Last year the IRS failed to inform Congress for several months after officials learned that now-retired IRS official Lois Lerner’s computer hard drive had crashed in 2011 and subsequently been destroyed. That eliminated one important source for obtaining Ms. Lerner’s emails, which lawmakers had demanded through subpoenas. Ms. Lerner, who headed up the IRS division that oversees tax-exempt entities, has long been a focus of congressional investigations. Ms. Lerner, who retired in September 2013, has denied wrongdoing in the matter. In a written statement Monday, the IRS said the agency and Mr. Koskinen “have been cooperative and truthful with the numerous investigations under way.” In the latest revelation, the IRS inspector general reported last month that IRS workers also had destroyed backup tapes that contained Ms. Lerner’s emails from 2010 and 2011. That occurred despite an order to workers by top IRS officials to preserve all potential evidence relating to the congressional probes. As a result, up to 24,000 Lerner emails were lost, the inspector general estimated. The inspector general’s office is a unit of the Treasury Department and independent of the IRS. The backup tapes were destroyed in March 2014, long after lawmakers started demanding Ms. Lerner’s emails. The inspector general said his office found no evidence that the destruction of the backup tapes was part of a willful effort to destroy evidence, however.   In his letter to Mr. Obama, Mr. Chaffetz cites a provision of the tax law that says that the IRS commissioner “may be removed at the will of the president.” “His obstruction takes the form of failure to comply with a congressional subpoena, failure to testify truthfully, and failure to preserve and produce up to 24,000 emails relevant to the investigation,” Mr. Chaffetz wrote. “We ask that you exercise your authority under [the law] to remove John Koskinen as commissioner of the IRS.” The targeting controversy erupted in May of 2013, when the IRS inspector general released a report finding that the agency used inappropriate criteria starting in 2010 to select conservative tea party-type groups for unusual scrutiny and lengthy delays when they applied for tax-exempt status.