Question: Which occurred first, St. Elizabeths Hospital being designated a National Historic Landmark or Sibley Memorial Hospital being a part of Johns Hopkins Medicine?

Context articles: Douglass (Washington, D.C.)
Johns Hopkins School of Medicine
Johns Hopkins Hospital
Suburban Hospital
Sibley Memorial Hospital
St. Elizabeths Hospital
Paul B. Rothman
William H. Welch House
Johns Hopkins University
William H. Welch

Douglass is a residential neighborhood in Southeast Washington, D.C., on the eastern side of St. Elizabeths Hospital, on the border of the Congress Heights Metro Station.
 It is bounded by Suitland Parkway to the north and east, Alabama Avenue to the south, and the St. Elizabeths campus to the west.
The Johns Hopkins University School of Medicine (JHUSOM), located in Baltimore, Maryland, U.S., is the academic medical teaching and research arm of Johns Hopkins University.
 Johns Hopkins has consistently been among the nation's top medical schools in the number of research grants awarded by the National Institutes of Health.
 Its main teaching hospital, the Johns Hopkins Hospital, is ranked the #3 hospital in the United States by "U.S. News & World Report".
The Johns Hopkins Hospital (JHH) is the teaching hospital and biomedical research facility of the Johns Hopkins School of Medicine, located in Baltimore, Maryland, U.S.
 It was founded in 1889 using money from a bequest by philanthropist Johns Hopkins.
 Johns Hopkins Hospital and the school of medicine are the founding institutions of modern American medicine and the birthplace of numerous medical traditions including rounds, residents and housestaff.
 Many medical specialties were formed at the hospital including neurosurgery, by Harvey Cushing; cardiac surgery by Alfred Blalock; and pediatrics and child psychiatry, by Leo Kanner.
Suburban Hospital is a community-based, not-for-profit hospital serving Montgomery County and the surrounding area since 1943.
 Located in Bethesda, Maryland, Suburban is the designated trauma center for Montgomery County.
 Suburban Hospital is affiliated with many local health-care organizations, including the National Institutes of Health.
 The hospital specializes in surgery, orthopedics, cardiology, neurology, oncology, emergency/trauma and a variety of additional clinical services.
 On June 30, 2009, Suburban Hospital became a member of Johns Hopkins Medicine.
Sibley Memorial Hospital is a non-profit hospital located in The Palisades neighborhood of Washington D.C. It is fully accredited by the Joint Commission on Accreditation of Healthcare Organizations, and is licensed by the District of Columbia Department of Health and Human Services.
 The hospital specializes in surgery, orthopedics, and oncology services.
 It has been part of Johns Hopkins Medicine since 2010.
St. Elizabeths Hospital opened in 1855 as the first federally operated psychiatric hospital in the United States.
 Housing over 8,000 patients at its peak in the 1950s, the hospital at one point had a fully functioning medical-surgical unit, a school of nursing, and accredited internships and psychiatric residencies.
 Its campus was designated a National Historic Landmark in 1990.
Paul B. Rothman (born 1958) is the Frances Watt Baker, M.D., and Lenox D. Baker Jr., M.D., Dean of the Medical Faculty, vice president for medicine of Johns Hopkins University, and CEO of Johns Hopkins Medicine.
 As dean and CEO, Rothman oversees both the School of Medicine and the Johns Hopkins Health System, which together encompass six hospitals, hundreds of faculty and community physicians and a self-funded health plan.
The William H. Welch House is a three-story rowhouse located at 935 St. Paul Street in Baltimore, Maryland.
 Probably built in the 1880s, it is notable as the residence of William H. Welch (1850-1934) from 1891 to 1908.
 Welch was one of the "Big Four" founding professors at Johns Hopkins Hospital, and an important conduit of European medical research methods and ideas to the United States.
 He was also the first dean of the Johns Hopkins University School of Medicine and the first director of the Johns Hopkins School of Hygiene and Public Health.
 The house was designated a National Historic Landmark in 1976, and is included in the Baltimore National Heritage Area.
The Johns Hopkins University (commonly referred to as Johns Hopkins, JHU, or simply Hopkins) is an American private research university in Baltimore, Maryland.
 Founded in 1876, the university was named for its first benefactor, the American entrepreneur, abolitionist, and philanthropist Johns Hopkins.
 His $7 million bequest—of which half financed the establishment of Johns Hopkins Hospital—was the largest philanthropic gift in the history of the United States at that time.
 Daniel Coit Gilman, who was inaugurated as the institution's first president on February 22, 1876, led the university to revolutionize higher education in the U.S. by integrating teaching and research.
 Adopting the concept of a graduate school from Germany's ancient Heidelberg University, Johns Hopkins University is considered the first research university in the United States.
William Henry Welch (April 8, 1850 – April 30, 1934) was an American physician, pathologist, bacteriologist, and medical school administrator.
 He was one of the "Big Four" founding professors at the Johns Hopkins Hospital.
 He was the first dean of the Johns Hopkins School of Medicine and was also the founder of the Johns Hopkins School of Hygiene and Public Health, the first school of public health in the country.
 Welch was more known for his cogent summations of current scientific work, than his own scientific research.
 The Johns Hopkins medical school library is also named after Welch.
 In his lifetime he was called "the Dean of American Medicine" and received various awards and honors throughout his lifetime, and posthumously.