How does border security or limits on immigration prepare the US for taking in large numbers of climate refugees? The US's strengths when it comes to immigration is specifically that we're relatively easy to get into for a rich country, because we have a generous family reunification visa program, and thus have large support communities for basically every immigrant population you can think of.

In other words, the US is already way more prepared for climate refugees than, say, the EU is. Though, to be fair, the US is also going to have a lot of internal climate refugees, too.