If you are a skeptic, it works the exact opposite. The argument works now as there hasn't been a process that involves the fair presentation of all the evidence. Until that time, it is you who is choosing to believe something without all the evidence.
The process you describe is that involved in obtaining a criminal conviction- which I suspect will indeed occur eventually in the case of the Trump administration. However it is certainly fair to reach a reasonable working conclusion before that. Indeed it is essential to do so all the time just to lead our lives. We get a phone call telling us we owe the IRS $2453 and that we will go to jail if we don't send them Apple Music Store gift cards? We conclude it is probably a scam without a fair presentation of all the evidence. The ground outside is wet and we see many people with umbrellas? We conclude it probably rained, without a detailed investigation of possible other causes. We are entitled, indeed often have to make these likely conclusions based on reasonable evidence all the time. To hold a reasonable opinion does not need the rigid requirements for criminal conviction or indeed for scientific publication. And holding a reasonable opinion adoes not exclude the expectation of changing it if new evidence arises. Being a skeptic does not mean having a completely blank mind until some theoretical, absolute level of proof is obtained.
By the way- the level of evidence that individuals in the Trump campaign coordinated with Russia is already such that maintaining otherwise is what is unreasonable. Claims that there is no evidence are laughable!
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