https://www.aoc.gov/nations-stage/lying-state-honor
The Rotunda of the U.S. Capitol has been considered the most suitable place for the nation to pay final tribute to its most eminent citizens by having their remains lay in state (in the case of government officials and military officers) or in honor (in the case of private citizens). Since 1865, most services have used the catafalque constructed for the coffin of Abraham Lincoln.
These occasions are either authorized by a congressional resolution or approved by the congressional leadership, when permission is granted by survivors. When the Architect of the Capitol (AOC) is notified that a ceremony will occur, teams are coordinated across the Capitol campus and a commitment to excellence ensures that no detail is overlooked.
————
https://www.cnn.com/2018/08/26/politics/mccain-lain-state-capitol/index.html
(CNN)Sen. John McCain, whose more than three-decade career in the Senate irreversibly impacted the tenor of Washington, will lie in state in the US Capitol this week, an honor given to few statesmen.
Senate Majority Leader Mitch McConnell, a longtime ally of McCain, said that the decision came "in coordination with Speaker of the House Paul Ryan, Senate Democratic Leader Chuck Schumer and House Democratic Leader Nancy Pelosi."