  It has been conjectured that an impurity with charge Z greater or equal to 2
can be localized due to its interaction with electrons in a metal. The simplest
case is an impurity free to move between only two sites, which interacts
locally with s-wave electrons. For Z greater or equal to 2 the hopping of the
impurity is formally irrelevant and this has been argued to lead to
localization. In this paper it is shown that other processes, in particular
joint hopping of the impurity and one or more electrons between the sites, play
an important role and have not been treated properly in the literature. Being
relevant in a renormalization group sense, even when Z greater or equal to 2,
these terms lead to delocalization of the impurity. Using bosonization, it is
shown how these processes are generated from marginal operators that are
usually neglected and the dangers of ignoring marginal or irrelevant operators
are discussed in detail. Questions about implications for the more general
situation of many sites to which the impurity can hop, are also considered.
