The acquittal of Thomas J. Barrack Jr., a former Trump adviser, showed the difficulty of proving wrongdoing amid a brew of political, personal and commercial interests.
Thomas J. Barrack Jr., a Los Angeles businessman and friend of the former president, had been accused of working on behalf of the oil-rich nation without disclosing it.
Documents show that the Justice Department has records indicating that John Allen, who now heads the Brookings Institution, secretly lobbied for Qatar and lied about it to federal agents.