weak part
weak spot
soft spot

I tried by intelligence to overcome and build up the weak part of my body.

David Taylor has directed a fine cast in which there is not a weak part.

For that reason, the Russian plan was to break through a weak part of the line.

Your fine mind put to our use, to find the weak parts of our plan.

I had scarcely explained it to him before he discovered its weak part.

She added, though, that the Chancellor hoped to focus on middle schools because he considered them a weak part of the system.

Observing that the German left was the weaker part of their line he concentrated his forces there.

We're all part of it, child, adult, weak or strong.

He also repeated the rhythm by time and a half, leaving the weak part of the second beat silent.

Once the families break up, there is so much switching around that weaker parts read a bit like a game of musical houses.