It remained unclear exactly what the investigators may have been looking for, but Mr. Clark was central to President Donald J. Trump’s unsuccessful effort in late 2020 to strong-arm the nation’s top prosecutors into supporting his claims of election fraud.

The law enforcement action at Mr. Clark’s home in suburban Virginia came just one day before the House committee investigating the Jan. 6, 2021, attack on the Capitol was poised to hold a hearing examining Mr. Trump’s efforts to pressure the Justice Department after his election defeat.

The hearing was expected to explore Mr. Clark’s role in helping Mr. Trump bend the department to his will and ultimately help in a bid to persuade officials in several key swing states to change the outcome of their election results.