  We discuss the low energy theory of two-dimensional metals near the onset of
spin density wave order. It is well known that such a metal has a
superconducting instability induced by the formation of spin-singlet pairs of
electrons, with the pairing amplitude changing sign between regions of the
Fermi surface connected by the spin density wave ordering wavevector. Here we
review recent arguments that there is an additional instability which is nearly
as strong: towards the onset of a modulated bond order which is locally an
Ising-nematic order. This new instability is a consequence of an emergent
"pseudospin" symmetry of the low energy theory---the symmetry maps the
sign-changing pairing amplitude to the bond order parameter.
