I cannot stress this enough. While you can't legally lie to a cop, they can lie to you. Be very careful when it comes to them trying gain access to your vehicle. There are tricks. Never allow them to search your car, ever, even if they threaten you with the stupid drug dog. It's a feingned attempt to intimidate you.
The cop stated that "if I want to stop you, all I have to do is follow you. If I follow you long enough you're going to get nervous and make a mistake. Then I have a legal reason to stop you".
Only experience can get you passed this. They call this "blue light fright". The cop will put his pig head on your bumper in an attempt scare you into a mistake. Eventually, especially if your're impaired, you will use your side mirror in an effort to id who is behind you. In the process you might hit the white line and then he has you. To get to this point, you were probably profiled for some reason. Maybe it was the look on your face, your car, the time of day, who knows. The point is he really wants to look in your vehicle and he can't do that without pulling you over constitutionally.