[6] During his time in private practice, Corcoran served as: trial counsel for an insurer in a $4 billion insurance coverage case that followed the destruction of the World Trade Center,[6] a government contract litigation in which he represented Computer Sciences Corporation; a lead counsel for the audit committee of the largest pharmaceutical care company in the United States; a class action litigation in Hawaii in which he defended Verizon; and an antitrust counsel in a case where he represented T-Mobile in a civil lawsuit accompanying the US DOJ action to enjoin its merger with AT&T.
[10] On May 10, 2022, Debra Steidel Wall, the acting Archivist of the United States, wrote Corcoran to reiterate that Trump had taken hundreds of pages of classified materials with him, including highly classified Special access programs materials, and that their extended negotiations over alleged executive privilege was delaying investigations and threat assessments already underway.
[12] On May 12, 2022, the DOJ issued a grand jury subpoena to the National Archives for the classified documents they had provided to the House select committee investigating the January 6 United States Capitol attack.
[13] In a letter to the DOJ dated May 25, 2022, Corcoran argued against proceeding with a criminal investigation, saying that presidents have the "absolute authority" to declassify documents.
[18] The Washington Post reported on “[m]onths of disputes” between DOJ prosecutors and FBI agents “as both sides wrestled with a national security case that ha[d] potentially far-reaching political consequences."
In 2022, Trump's Save America political action committee paid Corcoran's law firm $1.2 million in legal fees.
[21] In January 2023, Corcoran was subpoenaed and appeared before a grand jury and testified for about four hours, but he invoked attorney–client privilege to avoid answering certain questions about his conversations with President Trump.
[30] In May 2023, the Guardian reported that Corcoran had told associates he believed he had been misled when he searched Mar-a-Lago for classified documents in response to the subpoena.
When the FBI returned months later with a search warrant, agents found classified documents located in Trump's office, among other places.
[31] After the indictment of President Trump, Corcoran’s notes were at the center of a legal battle in the classified documents case, and Judge Aileen Cannon, the judge overseeing the case, heard arguments from the parties on whether “to limit prosecutors' use of the notes and to have the entire case dismissed based on the role of the notes in the government's case.”[32] On August 24, 2023, Corcoran accompanied President Trump to his arraignment in the U.S. District Court for the District of Columbia, on separate federal charges brought by special counsel Jack Smith relating to efforts to overturn the 2020 presidential election.