I agree. In fact the Immigration issue is Bush's only ace-in-the-hole; but I'm afraid he won't play it, allowing that issue to default to the Democrat Candidate (Hillary! God forbid). In my nightmares I can hear that witch next October screaming: "Elect me ... I'll close those borders!"(Of course she won't, but her workers will cheer loudly, and the American voters will scream: "YES!")
I'm not sure the Democrats are smart enough to steal it, though, and it also causes some problems with them holding their coalition together.
On the other hand, it costs the GOP virtually nothing (politically speaking), and gains them huge numbers of concerned voters.