be onto a winner
If you are onto a winner, you are doing something that is likely to succeed.
You're onto a winner with that idea— Vas a triunfar con esa idea
We knew we were onto a winner when we saw the crowd's reaction— Supimos que íbamos a triunfar cuando vimos la reacción del público
Trump knows he's onto a winner with his inflammatory comments — Trump sabe que ha acertado con sus comentarios incendiarios