When the elections were held

Can one say
a. The crisis in December was not severe.
b. The crisis was not severe in December.

I would think the first one is talking about a crisis that took place in December and the second one does not say when the crisis started but is simply stating that in December it was not severe.

Could (a) be used instead of (b)? Is it ambiguous.

c. The crisis when the elections were held was not severe.
d. The crisis was not severe when the elections were held.

Here again I have the same question. The first one I would say seems to suggest that the crisis took place when the elections were held and was probably caused by it. The second one says nothing about when the crisis started. But could (c) be used instead of (d)?

Many thanks.