A corrupt bureaucracy, loss of the Rule of Law, and vast illegal immigration. Sound familiar? Heck, it is the official policy of the democrat party.
Rome did fall in a day. It was the day Caesar crossed the Rubicon with his army. From that point on it became a dictatorship. The dictatorship led to such flagrant public spending that the Empire could no longer afford the tax burdens. You actually had people placing themselves into slavery just to escape from the crushing taxes of the day.
It happens again and again to Empire after Empire but the typical historian is blind to it because most of them like governments which tax and spend allot.