亲,我感觉,这是一个错句.正确的表达是:
One protestor said that the government could have done something to stop the spread of the demonstration BEFORE they took effictive steps.
理由:这是虚拟语气,改写成非虚拟语气句,就是:
The government DIDN'T DO anything to stop the spread of the demonstration before / when they did take effictive steps.