Question: What U.S. President frequently visited a restaurant near the old Spanish mission in colonial "Las Californias"?

Context paragraphs:
Fernando Rivera y Moncada: Fernando Javier Rivera y Moncada (c. 1725 – July 18, 1781), born in Mexico, was a soldier of the Spanish Empire in New Spain.  He served in the far north-western frontier of New Spain, in The Californias ("Las Californias"), participating in several early overland explorations.  Fernando Rivera y Moncada served as third Governor of The Californias, from 1774-1777.

José de los Reyes Berreyesa: José de los Reyes Berreyesa, also spelled Berrelleza (6 January 1785−28 June 1846), was born at Mission Santa Clara de Asís in Las Californias province of the Spanish Viceroyalty of New Spain (colonial México).

Las Flores Estancia: The Las Flores Estancia (also known as Las Flores Asistencia) was established in 1823 as an "estancia" ("station").  It was part of the Spanish missions, asistencias, and estancias system in Las Californias—Alta California.  Las Flores Estancia was situated approximately halfway between Mission San Luis Rey de Francia and Mission San Juan Capistrano.  It is located near Bell Canyon on the Camp Pendleton Marine Corps Base ten miles south of the City of San Clemente in northern San Diego County, California.

Pious Fund of the Californias: The Pious Fund of the Californias, Spanish: "Fondo Piadoso de las Californias" is a fund, originating in 1697, to sponsor the Roman Catholic Jesuit Spanish missions in Baja California, and Franciscan Spanish missions in Alta California in the Viceroyalty of New Spain from 1769 to 1823, and originally administered by the Jesuits.  It became the object of litigation between the US and Mexican governments in the 19th century, with the resolution making legal history in The Hague in 1902.

San Antonio de Pala Asistencia: The San Antonio de Pala Asistencia, or the "Pala Mission", was founded on June 13, 1816 as an "asistencia" ("sub-mission") to Mission San Luis Rey de Francia, some twenty miles inland upstream from the latter mission on the San Luis Rey River.  Pala Mission was part of the Spanish missions, asistencias, and estancias system in Las Californias—Alta California.  Today it is located in the Pala Indian Reservation located in northern San Diego County, with the official name of Mission San Antonio de Pala.  It is the only historic mission facility still serving a Mission Indian tribe.

El Adobe de Capistrano: El Adobe de Capistrano, or simply known as El Adobe, is a restaurant located in San Juan Capistrano, California.  It has been operated since 1948 and is in a building composed of two historic adobes near Mission San Juan Capistrano.  It is also famous for being frequented by and being a favorite of U.S. President Richard Nixon who lived in nearby San Clemente.

Mission San Juan Capistrano: Mission San Juan Capistrano was a Spanish mission in colonial "Las Californias".  Its ruins are located in present-day San Juan Capistrano, Orange County, southern California.

The Californias: The Californias, or Province of the Californias, or Spanish: Las Californias, Provincia de las Californias (1768–1804), was the northwestern-most area of the Viceroyalty of New Spain (comprising Spain's colonial possessions in the Western Hemisphere and Pacific Spanish East Indies).

El Camino Viejo: El Camino Viejo a Los Ángeles (English: the Old Road to Los Angeles ), also known as El Camino Viejo and the Old Los Angeles Trail, was the oldest north-south trail in the interior of Spanish colonial Las Californias (1769–1822) and Mexican Alta California (1822–1848), present day California.  It became a well established inland route, and an alternative to the coastal El Camino Real trail used since the 1770s in the period.

Manuel Dominguez: Manuel Dominguez (1803–1882) was born at Mission San Juan Capistrano, in the colonial Las Californias province of the Spanish Viceroyalty of New Spain (colonial México).  He was the heir to the vast Rancho San Pedro land grant in the Los Angeles Basin.

Supporting paragraphs: El Adobe de Capistrano Mission San Juan Capistrano
Answer: U.S. President Richard Nixon