You need the bob to have angular velocity $\omega$ such that the centripetal force keeps the bob at distance P from the center.

If this is done exactly T2=0 and it will be "just taut".

You can work your force equations to find out what value of $\omega$ keeps your bob at distance P from the center.

Remember $a_c = \omega^2 r$ where $a_c$ is the centripetal acceleration, $\omega$ is the angular velocity, and $r$ is the radius of the circular motion.