An extremal horizon can be always embedded into spacetime as a Killing
horizon but usually not uniquely. For example, extremal
Reissner-Nordstrom and Majumdar-Papapetrou black holes are two different
asymptotically flat spacetimes with the same geometry induced on their
horizons. We consider an infinitesimal version of this
problem—classification of connections admissible on the horizon in
Einstein-Maxwell theory. We can interpret them as specific zero modes in
the corresponding Near Horizon spacetime. Surprisingly enough, for
spherically symmetric backgrounds those connections are basically unique
unless we fine-tune the charge and cosmological constant. We also
discuss how this uniqueness extends into the whole spacetime under an
assumption of analyticity.