**(a) Nonlinear mobilization — the salience threshold.**
Replace linear $\alpha D$ with a saturating, sigmoid response:
$$
\dot E = \frac{\alpha D^n}{K^n + D^n} - \mu(E-E_0)
$$
This captures a *political salience threshold*: small-scale fraud generates no response (below public attention), while fraud past a critical visibility triggers sharp mobilization. The Hill exponent *n* measures how threshold-like public/regulatory attention is. This makes the model far more realistic and adds a second bifurcation parameter.