From the end of that interview
Finch built a machine that basically causes a bunch of potential terrorists to be murdered. But he wasn't willing to kill one corrupt Congressman to save thousands.
Note he says "causes", not "calls for".
The machine identifies an event that will result in the loss of life of human beings. (And then Harold had to make it discern between terrorist events and everything else, for the government.)
It then spits out the number or numbers of people who are central to the event. For relevant numbers we assume that they're perpetrators based on what we've seen Control do, but as we've seen from irrelevant numbers it could be perpetrator or victims. The second to last episode had five numbers, and iirc they were Relevant from Root, yet they were immediate victims. If the machine spat out kill lists, why didn't it give the numbers of Collier and crew instead?
Well, Vigilance is anti-surveillance, they take particular actions that happen cause them to be difficult to be seen by the machine. Furthermore, if you really want to get to who's responsible, for so much loss of life up to now and Samaritan going forward, why hasn't the machine given up Greer? Putting a bullet in his skull a season ago would save a lot of trouble. (Alternately, why wasn't Collier's number given, he was ultimately a victim too, in addition to perpetrator.) We saw how he evaded Root, the man is a fucking spy.
I make this as a case of the machine having incomplete information.
(There's also HR. Remember the head was particularly secretive and circumspect about running the thing. So while taking him out solves the whole problem, if the machine can't see him... There's also the lady they couldn't save in the reunion episode, there was not enough time between the machine giving the number and the event happening (it was a Vigilance op), yet for other numbers we've seen cases where at the start of the episode the team is expositing that they've spent days or even weeks doing surveillance since they got the number.)
Wait, shit, this is a tangent.
Anyways, machine sees event that causes a loss of life, provides numbers as to what it knows. It never says kill, it doesn't even say responsible, it just says involved.
It is Control, it is
people, who decide that the expedient solution is murder. In the case of relevant numbers, once you find the people responsible for the event, you don't
need to kill them. They are dead to rights responsible for planning a (nasty) crime, you could justifiably lock them up.
They didn't need to kill the senator, that just was what Reese jumped too. They could have tried outing him for the insider trading deal, or any other number of things so that he would no longer be in a position to be of use in the rise of Samaritan.
The machine didn't say kill, Reese said kill, the machine just said involved.