barrelling is a term borrowed from
long-standing United States political practice.
As that hyperlink
shows, it is associated with electoral systems
where candidates likely to form part of a
government who are standing in closely-contested
'marginal' electoral districts seek electoral
benefit by promising substantial spending if
they are elected and their party becomes the
government party. Most districts are not
marginal, instead being safe for one of the two
major electoral groupings in such contests.