There's a ridiculous myth that RINOs in DC have been spinning about illegal immigration and it goes something like this: Hispanics vote almost entirely based on the illegal immigration issue and if Republicans deliver an amnesty, Hispanics will be so grateful that the percentage of them voting Republican will go from roughly 30% up to 50+%.
So, even if we allow 12-20 million mostly uneducated, mostly Hispanic illegal aliens from socialist countries to become Americans and that leads to another 30-40 million (or more) of their relatives becoming U.S. citizens through chain migration, it'll still be a net gain for the GOP because they'll be voting majority Republican.
Laugh if you want, but there are "bubble Republicans" in D.C. that believe this. If they didn't, they certainly wouldn't be setting up a situation where the GOP could be demographically overwhelmed to such an extent via illegal immigration that we'd be forced to have a Democrat-lite agenda to keep ourselves from becoming a permanent minority party.
On the other hand, it's also worth noting that the Democrats clearly believe that they're going to be the ones to benefit politically from turning illegals into American citizens. That's the driving force behind their push for an amnesty and their desire to keep the floodgates on our southern borders open.
That brings us to John McCain's presidential campaign.
No Republican is more closely associated with amnesty than John McCain. He was so heavily tied to the comprehensive immigration bill that was stopped in the Senate that many people called it the McCain/Kennedy bill. Furthermore, although he switched to a security first position so he'd have a chance to win the GOP primaries, McCain still explicitly said that he intended to put illegals on a path to citizenship after the border was secured. Since then, McCain has flip-flopped back and forth several times between his "security then amnesty" position and the "amnesty/we'll have border security, I swear, wink, wink" position AKA comprehensive immigration reform, but he clearly seems to be leaning towards the latter option.
With that in mind, if your highest priority is having open borders and amnesty, you couldn't possibly do better than John McCain as a Republican nominee. That's a fair statement, right? He has been the champion of that sort of legislation and his nod toward securing the border has been as close to the bare minimum as any Republican candidate could possibly pull off in a presidential election these days.