White House, Cheney's office, subpoenaed

The probe, in its sixth month, began with an investigation into whether administration officials ordered the firings of eight federal prosecutors, for political reasons.

But with senators of both parties already concerned about the constitutionality of the administration's efforts to root out terrorism suspects in the United States, the committee shifted to the broader question of Gonzales' stewardship of Justice and, in particular, his willingness to permit the wiretapping program.

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