I was wondering what various figures of speech could be used to describe a situation where somebody exploits a situation in order to push their own agenda. For example in Persian we have 'Catching a fish from muddy water'. Are there any English equivalents?

EDIT

Per request, let me clarify further what I have in mind:

I'm looking for a figure of speech used to describe a situation: say something happens, and the previously dogmatic opinion of somebody about the something, could then be somewhat justified after an accident, and that person would gloat and say 'I told you so', much like politicians would do from a given incident and use the turn of events to justify their own agenda. What idiom could you then use to reply to that person? Like 'You're really [idiom about opportunistically exploiting] now'.

A real example here:

Politician A and B are engaged in a debate. Politician A has been running the country for the past 4 years and has been lenient toward gun control, whereas politician B and his party have been critical of this leniency from the outset. During these 4 years under Politican A's reign, society has been very safe and healthy, with no gun crime whatsoever, and the population have actually been happy with Politcian A's gun policies. A month before elections, a psychotic army conscript starts shooting at people in the street and kills 2 people. Politician B will then launch a scathing attack on Politcian A for being reckless in his decision making and not heeding the advice of others, intentionally failing to point to the fact that the person committing the crime is an army personnel and has had his guns for a long time, and would have had his weapons with or without a stringent nationwide gun policy.

What would be a good figure of speech to describe Politician B's exploit of the incident to his own advantage?