How do you handle a once high-flying partner, who is no longer performing at the same levels ?

I would first want to find out why they are not performing anymore. Has the contact person changed which disrupted the relationship, did they start focusing on a competitor, have we neglected them, did they make any bad experiences with us or in projects, is there an economic reason…? It is important that you (re-)connect with that partner and ask these questions, maybe in the format of a retro (what went well, what didn’t, how to continue?). Once you know the reason and this is still a partner who wants to re-engage with you and sees the potential of the partnership, work on what broke it and make it a good partnership again. You would need to rebuild trust and re-take this partner through your partner journey. Once you experience success together again, the partnership will start flourishing again.