“The president has the sole authority to be able to make those recommendations and to execute that,” said Brandon Rottinghaus, Professor of Political Science at the University of Houston. Rottinghaus says that includes when and how long to keep the American flag at half-staff. “Typically, the nature of the tragedy will dictate how long it is left down,” he says. Because state and local flags aren’t allowed to fly above the American flag, they get lowered, too. The U.S. Flag Code says the American flag should fly half-mast for part of Memorial Day, and by the president’s order after the death of government officials. Historically, it’s been ordered lowered after the death of public figures, most recently, former First Lady Barbara Bush. “One opportunity for the President to be able to really connect to the American people is through the use of the flag,” said Rottinghaus, who says usage of the flag as a tool to rally the public increased during the Reagan administration.

https://www.khou.com/article/news/local/what-are-the-rules-for-lowering-flags-to-half-staff/285-570486827