It is legal to show up at a port of entry without any sort of anything. If all it allows you to do is show up at the port of entry it's a worthless scrap of paper.

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khuey a day ago | parent | next [-]

If you show up at a US port of entry without any sort of anything the default decision is to deny entry (exceptions for Canadian citizens and citizens of a few small islands). If you show up at a US port of entry with an ESTA/visa you will most likely be allowed entry. Refusals are relatively rare.

Commercial carriers such as airlines are also not allowed to transport people who need ESTAs/visas and do not have them to the US, so in practice it's relatively difficult to even get to the port of entry without a visa.

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anvuong a day ago | parent | prev | next [-]

Not for airlines and international cruise ships with US as destination. The attendants won't let you board unless you have a valid US visas. Carriers get fined if they transport individuals with no proper documents to a US port of entry.

	▲	mothballed a day ago \| parent [-]
		Airlines are fined for inadmissible passengers. Whether they have a visa or not. If they have no visa but are admitted there is no such fine. The visa is immaterial to the fine unless it conveys something beyond merely allowing you to present at a port of entry, which is allowed to basically everyone.

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bluGill a day ago | parent | prev [-]

In practice if you have the VISA they will almost always admit you. If you are rejected it generally means they find something at the border.