spoil, damage, or weaken something
vitiate - damage
When you ‘vitiate’ something, you corrupt it or make it less effective. This formal word, therefore, implies a destruction of purity or validity, and is most commonly used in a professional context, particularly in relation to legal agreements or contracts. It is also important to note that despite its spelling, the first syllable of ‘vitiate’ is pronounced ‘vish'.
Any changes we make to the policy at this late stage may vitiate the entire document.
A lack of trust between the two parties caused the vitiation of their contract negotiations.
Many in the country believe that one proven example of fraud is enough to vitiate the entire election.