  The electromagnetic theory of the strongly driven ion-temperature-gradient
(ITG) instability in magnetically confined toroidal plasmas is developed.
Stabilizing and destabilizing effects are identified, and a critical
$\beta_{e}$ (the ratio of the electron to magnetic pressure) for stabilization
of the toroidal branch of the mode is calculated for magnetic equilibria
independent of the coordinate along the magnetic field. Its scaling is
$\beta_{e}\sim L_{Te}/R,$ where $L_{Te}$ is the characteristic electron
temperature gradient length, and $R$ the major radius of the torus. We
conjecture that a fast particle population can cause a similar stabilization
due to its contribution to the equilibrium pressure gradient. For sheared
equilibria, the boundary of marginal stability of the electromagnetic
correction to the electrostatic mode is also given. For a general magnetic
equilibrium, we find a critical length (for electromagnetic stabilization) of
the extent of the unfavourable curvature along the magnetic field. This is a
decreasing function of the local magnetic shear.
