Investigators have also questioned witnesses about whether Michael T. Flynn was secretly paid by the Turkish government in the final months of the 2016 presidential campaign.
At least some of the subpoenas were related to Michael T. Flynn, the former national security adviser, but whether any related to other Trump campaign members was unclear.
Lt. Gen. H. R. McMaster, who succeeded Mr. Flynn as national security adviser, has slowly been removing some of his appointees, angering conservatives.
Citing grounds for a charge of obstruction of justice, Representative Brad Sherman introduced a proposed article of impeachment. But his efforts have virtually no chance of succeeding.
The attorney general is expected to face questions Tuesday over his interactions with Russian officials and role in the firing of James B. Comey as F.B.I. director.