The tensor analyzing power of the process [Formula Presented] for forward deuteron scattering in the momentum interval 3.7 to [Formula Presented] is studied in the framework of [Formula Presented] exchange in an algebraic collective model for the electroexcitation of nucleon resonances. We point out a special sensitivity of the tensor analyzing power to the isoscalar longitudinal form factor of the Roper resonance excitation. The main argument is that the [Formula Presented] and [Formula Presented] resonances have only isovector longitudinal form factors. It is the longitudinal form factor of the Roper excitation, which plays an important role in the t dependence of the tensor analyzing power. We discuss possible evidence of swelling of hadrons with increasing excitation energy.