Such routine oversight hearings have become a forum for lawmakers to air their grievances and seek to bolster an inquiry into the president based on inconclusive evidence.
Thomas Sobocinski, an F.B.I. agent, told House investigators that the prosecutor overseeing the investigation into the president’s son never said he did not have full authority to pursue charges.
The launch of an inquiry into Fani Willis, the Fulton County, Ga., district attorney, was the latest example of how the former president’s allies in Congress are using their majority to try to protect him.
Although some G.O.P. lawmakers see the appointment of David C. Weiss as a vindication of their strategy, others criticize the now-scuttled plea deal he struck with Mr. Biden.
Empower Oversight, a group of lawyers including former aides to Senator Charles E. Grassley, Republican of Iowa, is part of a constellation of groups facilitating G.O.P. investigations in Congress.