Your intelligence strength rests on a base drawn from your population and development; how many agents you can keep in the field comes from your intelligence budget. Cut the budget and the strength falls with it.
Espionage, sabotage, strike agitation and stirring up the public. Two separate dice are rolled: one decides whether the job lands, the other whether anyone traces it back to you — an operation can succeed and still be exposed.
With enough evidence you can cover it up, watch quietly, or condemn them publicly. Condemning on partial evidence is a gamble: pick the wrong country and the real culprit walks away untouched while your relations with the accused sour.
Counter-intelligence lowers the odds that an incoming operation lands and raises the chance the culprit is exposed. Raising the budget grows your offense and your defense together.