Sam Callahan | People | Arnold & Porter

Sam Callahan, former Senior Counsel in the White House Office of Management and Budget (OMB), helps companies, trade associations, nonprofit organizations, and public officials navigate consequential federal government action.

Sam advises clients across the full life cycle of federal government disputes—from regulatory strategy and agency engagement through litigation and appeal. He helps clients decide where and when to engage the government, pursue negotiated solutions where possible, build the record for potential litigation, and challenge or defend government action in court. His practice encompasses administrative and constitutional law, federal funding and appropriations, government contracting, executive orders, and other forms of Executive Branch action.

Sam also helps lead the firm’s Administrative Law and Regulatory Litigation practice and is a co-founder and editor of its Major Questions blog. He separately leads major appeals and complex litigation across substantive areas, including insurance coverage, environmental law, the False Claims Act, and other high-stakes commercial disputes.

At OMB, Sam oversaw major APA litigation and advised on executive orders, regulations, appropriations, government contracting, and emerging-technology policy. He also oversaw OMB’s AI docket, including legal review of the Biden Administration’s AI executive orders and national security memoranda. Drawing on that experience, Sam has particular insight into presidential action and the legal issues that arise as major White House initiatives are developed, implemented across agencies, and defended in court.

Sam clerked for Judge Paul V. Niemeyer of the U.S. Court of Appeals for the Fourth Circuit and Judge Christopher R. Cooper of the U.S. District Court for the District of Columbia. He graduated magna cum laude from Harvard Law School, where he was an Executive Editor of the Harvard Law Review, and received degrees in economics and trumpet performance from Indiana University.

Focus Areas

Experience

Pharmaceutical manufacturers and trade associations on constitutional, statutory, and administrative-law issues arising from major federal drug-pricing initiatives, including federal efforts to impose most-favored-nation (MFN) prescription drug pricing.
AT&T in federal and state regulatory proceedings concerning landline-service obligations, including FCC proceedings addressing federal preemption and efforts to transition investment toward broadband and next-generation communications infrastructure.
Broadcasting stations on Federal Communications Commission compliance, regulatory strategy, and policy issues.
Honeywell in litigation presenting complex federal preemption and statutory-interpretation issues concerning alleged radioactive emissions from its Metropolis Works uranium-conversion facility.
Senator Mark Kelly in litigation challenging Department of Defense administrative proceedings arising from his statements concerning military operations, securing a preliminary injunction on First Amendment grounds. Kelly v. Hegseth, 2026 WL 391777 (D.D.C. Feb. 12, 2026).

Major nonprofit organizations on litigation strategy and novel regulatory issues arising from threatened federal actions affecting tax-exempt status under Section 501(c)(3) of the Internal Revenue Code.
Government contractors and grantees in litigation and counseling concerning federal funding freezes and other actions by the U.S. Agency for International Development and Department of State.
A national trade association in a successful APA challenge to novel federal emissions and fuel-consumption regulations, securing a stay and ultimately vacatur of the rules as exceeding the agencies’ statutory authority. Truck Trailer Manufacturers Ass’n v. EPA, 17 F.4th 1198 (D.C. Cir. 2021).
A property developer in successful appeal regarding an agency’s application of historic preservation law to a major redevelopment project. D.C. Preservation League v. Mayor’s Agent for Historic Preservation, 236 A.3d 373 (D.C. 2020).