One-Time Pad Vulnerabilities
If the key bits are shorter then the message you need to reuse some part of the previous key bits. If this is known, and we can assume by Kerckhoff Principles,
then the enemy can crib-drag on the same message. A more dedicated enemy will always try this case and also the reuse case; the same key is used with another message, too.

As an example;

m = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
k = KkkkkkkkkkkkkkkkkkkkkkkkKkkkkkkkkkkkkkkkkk


where $x$ represents the message bits, $k$ represents the key bits and $K$ represents the start of the key bits. Divide the message into parts;

m1 = xxxxxxxxxxxxxxxxxxxxxxxx
k  = Kkkkkkkkkkkkkkkkkkkkkkkk
m2 = xxxxxxxxxxxxxxxxxx
k  = Kkkkkkkkkkkkkkkkkk


now, execute crib-dragging.