Does ESTA ensure admission to the United States?
The acquisition of a travel authorization, only entitles you to travel to the U.S. without a Visa.
However, this authorization does not mean that you are eligible for U.S. entry.
In all cases, U.S. Customs, and Border Protection officers, determine your admissibility upon arrival at the ports of entry.
This inspection may reveal that you are inadmissible under the Visa Waiver Program, or for any other reason, that does not meet the legal, and regulatory requirements of the United States.