Sorry is the implication that the US is in the state it’s in because infected people are continuously walking across the border and infecting more people?
If no, then being an island isn’t really relevant here.
No, it’s because 100 different people (according to genetic studies) started separate chains of infections in New York City due to international travel, immediately overwhelming any efforts to do contact tracing.
I invite you to spend some time with Hawaii's COVID statistics before coming to the conclusion that being an island, or not, is irrelevant to US outcomes.
If no, then being an island isn’t really relevant here.