Consequently, neither congress nor the president would support the proposal and its heavy costs. which word in the sentence is a coordinating conjunction?

The coordinating conjunction in the sentence is NOR.

There are only seven coordinating conjunctions. Remember the terms FAN BOYS in relation to coordinating conjunctions.
F - for
A - and
N - nor
B - but
O - or
Y - yet
S - so

Coordinating conjunctions connect words, phrases, and clauses. Giving equal emphasis on two main clauses.

Here are the patterns for using coordinating conjunctions:
1) connecting two main clauses
main clause + coordinating conjunction + main clause

2) connecting two items
item + coordinating conjunction + item

3) connecting three or more items in a series
item + item +  coordinating conjunction + item