they showed that if the global integral from [@G] has a double pole, then a global integral involving an Eisenstein series on the other maximal parabolic subgroup of $G_2$ must be nonzero. They then showed that this global integral unfolds to a period integral which vanishes on every cuspidal representation of ${{\mathrm{GL}}}_3({{\mathbb {A}}}).$ When this argument is adapted to the nonsplit case the resulting period, which is on ${{\mathrm{SU}}}_{1,1},$ does [*not*]{} vanish on every cuspidal representation of ${{\mathrm {U}}}_{2,1}({{\mathbb {A}}}).$ Rather, it fails to vanish, by earlier work of Gelbart, Rogawski, and Soudry [@GeRoSo2], precisely on the image of an endoscopic lift constructed in [@RogawskiBook]. By carefully combining this information with information about the relationship between Rogawski’s liftings and the stable base change lift of Kim and Krishnamurthy [@KimKrishOdd; @KimKrishEven], as well as results about the image of that lift obtained by Ginzburg, Rallis and Soudry by the method of functorial descent [@GRSBook], we obtain the following main result.

Take $\pi$ a globally generic irreducible cuspidal automorphic representation of the quasisplit unitary group ${{\mathrm {U}}}_{2,1}({\mathbb{A}})$ attached to a quadratic extension $E$ of $F.$ Let $\chi_{E/F}$ be the quadratic character attached to $E/F$ by class field theory. Then $L^S(s, \pi, {{\mathrm{Ad}}})$ 