Not being well verses on campaign finance laws , I don't know if what Trump and Cohen did was illegal. But the guy you site using the word "likely" to describe the nature of the violations is unbecoming of someone who proclaims to know the law. It either is illegal or is not legal.
"That’s because – as someone who served for two years as a member of the Federal Election Commission – the campaign finance law violations that Cohen pleaded guilty to committing, allegedly at Donald Trump’s direction, aren’t really violations"
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"In addition, Cohen was sentenced on his guilty pleas to violating campaign finance law on Trump’s behalf – an action that, as I will explain, was not really a crime at all."
Cohen is a lawyer, and no doubt retained his own consul. So I find it hard to believe he would plead guilty and accept a 3 year jail term if what he did was not illegal.