Aldehydes without alpha hydrogens undergo Cannizzaro reaction in strongly alkaline conditions. However trihaloaldehydes undergo haloform reaction under the same conditions. I wonder what might be the reason?

Can you say what does the alkali do in this reaction?

Aldehydes without alpha hydrogens undergo Cannizzaro reaction in strongly alkaline conditions. However trihaloaldehydes undergo haloform reaction under the same conditions. I wonder what might be the reason?

The trihalo substituent is a good leaving group and dominates further reactions progress.