They are excluded, they already can't check the first box (either born in the US or naturalized). "And subject to the jurisdiction thereof" was added to exclude certain people born on US soil as per the USSC in 1898:
Children born to foreign diplomats who have diplomatic immunity are not subject to the jurisdiction of the United States.
Children of invading army members that have occupied and controlled some part of US territory, born on that occupied part of the United States are obviously not subject to the jurisdiction of the United States.
Members of Native American tribes were subject to the jurisdiction of their tribal governments and did not pay US taxes when the 14th amendment was passed and were then not subject to the jurisdiction of the United States.
So you have to check both boxes to be an American citizen:
Either the box 'born on US soil' or 'naturalized' AND the box 'subject to the jurisdiction of the United States'.
Whoever can check two boxes is a citizen.
Everyone else in the country only check one box. They are subject to the jurisdiction of the United States, but they are not born here nor are they naturalized. Their children born on US soil are citizens as per the 14th amendment.
But being naturalized doesn't mean your citizenship can never be revoked. Denaturalization is possible (not common!) for both immigrants and natural born citizens in the following cases:
Running for Public Office or Working in the Government of a Foreign Country
Serving in a Foreign Military
Committing an Act of Treason Against the U.S.
And for immigrants it is also possible to be denaturalized when:
You lie during the naturalization process (failure to disclose criminal activities, lying about your identity, willful misrepresentation), on your citizenship application, affidavit, or to a consular official. Even if USCIS doesn't catch you in a lie during the process, they may file a denaturalization action against you even after you gain citizenship.
You refuse to testify before a U.S. congressional committee investigating your alleged involvement in subversive acts. Subversive acts are those intended to harm U.S. officials or overthrow the U.S. government. The requirements to testify before Congress expire after ten years.
The U.S. government can prove that you joined a subversive organization like ISIS or Al Qaeda within five years of becoming a naturalized citizen.
You became naturalized by serving in the U.S. armed forces and you are dishonorably discharged before serving five years of military service.
You obtained citizenship illegally.
Trump will be going after illegals first and foremost, starting with the ones with severe crimes like murder, sexual assault and drugs- and human trafficking. After those are all gone they will start looking at the lesser offenses, including entering the United States illegally, which IS a crime. Then yes, I believe naturalized people might be at risk if they committed serious crimes. Any good citizen who did not commit any of the crimes above has nothing to fear. About 15% of the US population is naturalized, that is over 50 million people. Only a small handful of those 50 million have a reason to be worried.