If we are not mindful in the US, this experiment will follow the path of the Roman Empire that decayed from within, just as we are doing now.
Political corruption, oral corruption, widespread homosexuality, low birthrates, high immigrants, lack of respect for law, lack of respect for human life especially of the young and unborn, tax and spend politics, bread and circuses to keep the masses entertained while politicians raid the treasury is what brought down the Roman Empire long before the Goths invaded.
Any of that sound familiar?
It's more than familiar, it's almost a carbon copy. The same thing happened to the Byzantines. Although they outnumbered the Muhammadans 10-1, they were able to walk in and slaughter them at will because they became weak and foolish.
The problem with this theory is that it equally well defines conditions during not only the early Roman Empire at its height of power, but even during the last century or two of the Republic.
So why did the empire last for 400-500 years after these horrible tendencies developed? Based on a similar timeline, we have at least 400 years before we need to begin to seriously worry.