Actually, I'd argue that the American Heritage definition #1 applies in this case. The word coerce is a verb; the definition does not depend upon the success of the action -- it IS the action.

Wordnet says:

to cause to do through pressure or necessity, by physical, moral or intellectual means

dictionary.com says:

to dominate or control, esp. by exploiting fear, anxiety, etc.

The fact that they were booed out of the church doesn't mean they weren't trying to coerce the cardinal into doing the bidding of 6 "Catholic schoolgirls" with some leftover Halloween accoutrements.