\textbf{Understanding the MHD challenges for ITER Q}$=$\textbf{10 operation at reactor relevant conditions}.

DIII-D experiments to assess options for Q$=$10 operation in ITER without harmful core MHD nor ELMs have advanced both achieved parameters and understanding of present limitations. Q\textasciitilde 10 performance is achieved in low collisionality ($\nu $*) ELM-stable plasmas with small co-Ip NBI torque using RMP ELM suppression, and small counter-Ip NBI torque using QH-mode edge. Both ELM control approaches are limited by core instabilities, while the edge regime is strongly affected by local edge torque density. A rotation threshold for RMP ELM suppression corresponds to a critical radius for the ExB rotation zero-crossing, and this threshold can be crossed at widely varying net NBI torques. An ITER-relevant net NBI torque on DIII-D tends to produce a less ITER-relevant negative local edge torque density, with severe penalty for ELM suppression. In the QH-mode approach, negative edge torque density correlates with increased edge ExB shear obtained at low density, leading to improved confinement at low net NBI torque, and Q\textgreater 10 equivalent performance at q$_{\mathrm{95}}$\textasciitilde 3. However, low $\nu $* and low q lead to pressure peaking instabilities. The character of edge fluctuations in QH-mode is key to simultaneous low torque and low q$_{\mathrm{95}}$ operation: broadband fluctuations are compatible with low rotation, while a coherent edge harmonic oscillation (EHO) tends to lock to the wall. A recent discovery is that the plasma-wall separation gap controls the character of the edge fluctuations: smaller gap leads to higher-n EHO at low NBI torque; even smaller gap leads to broadband fluctuations. Too small an outer gap brings back ELMs, with the threshold gap depending on NBI energy, likely through a gyro-radius dependence of fast-ion-wall interactions. A large RF-heating fraction could overcome present limitations by reducing negative edge-torque density, wall interactions, and pressure peaking from strong core fueling.