  We use the method of gauging equations to construct the electromagnetic
current operator for the two-nucleon system in a theory with a finite cutoff.
The employed formulation ensures that the two-nucleon T-matrix and
corresponding five-point function, in the cutoff theory, are identical to the
ones formally defined by a reference theory without a cutoff. A feature of our
approach is that it effectively introduces a cutoff into the reference theory
in a way that maintains the long-range part of the exchange current operator;
for applications to effective field theory (EFT), this property is usually
sufficient to guarantee the predictive power of the resulting cutoff theory. In
addition, our approach leads to Ward-Takahashi (WT) identities that are linear
in the interactions.
  From the point of view of EFT's where such a WT identity is satisfied in the
reference theory, this ensures that gauge invariance in the cutoff theory is
maintained order by order in the expansion.
