A strict reading of the Constitution looks to outlaw searching anyone anywhere without a warrant, not just searching Americans. Might want to watch that slippery slope there, fella.
What you have to look at is what word the founders used to determine the scope; everywhere else in the document, the term, "the people" refers specifically to American citizens. If a provision is meant to apply to everyone in general, they used the words, "all persons" for covered actions, and "no persons" for things the government is prohibited from doing.
You can see this difference between the 4th and 5th Amendments; the 4th reads
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Whereas the 5th reads
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation."
As you can see, there is a blatant and actionable difference between the meaning of those two Amendments - the first one implicitly states that it applies only to citizens, whereas the second obviously applies to everyone within US government jurisdiction.
The only slippery slope here is the one where people think they can re-interpret the meanings of 250 year old words with modern language, ie references to the term "regulated" in the 2nd Amendment.