Excerpts of the President's News Conference
I think that some of the Marines are at Shanghai for the purpose of protecting American lives and property, and they will be used to whatever extent it is necessary that they should be used for that purpose. That is the only purpose that America ever lands any Marines on foreign soil and they would have no other purpose in the present situation. You can get more detailed information I think from the Secretary of State's office, or from the Secretary of the Navy, than I have. I know that we have some war vessels in the harbor at Shanghai, and I think one or two others on the way there. Though we know—I know of nothing serious that has happened to any American citizens or any American property, but on account of the disorder there it is considered that they are in jeopardy and Marines have been landed in order that they may have proper and ample protection. That is all the action that I know of that is contemplated in relation to China or Chinese territory.
Source: "The Talkative President: The Off-the-Record Press Conferences of Calvin Coolidge". eds. Howard H. Quint & Robert H. Ferrell. The University Massachusetts Press. 1964.
Calvin Coolidge, Excerpts of the President's News Conference Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/349109