Blend in with who?

With the many thousands of people who are showing up at the border.

Again, it's not hard to pick out the one guy who speaks only Arabic, and doesn't speak a word of Spanish. And if that guy doesn't have any ID at all, he's not going to get treated the same way as the hundreds of thousands of central american migrants who are getting processed.

That's the point - if you're trying to get over the border unnoticed, you're better off being one of the thousands and thousands of Arabic-speaking nationals who fly into New York or DC every day and passing through an ordinary customs counter, rather than being one of the three or four dozen Arabic-speaking nationals who show up at the southern border claiming asylum. Get a fake passport and fly in - there's no benefit at all to trying to go through the asylum process, and a massive amount of risk.