I realized I've been thinking about this case all wrong.
As I've noted, I can't get myself all worked up about "illegal campaign contributions". Hush money isn't really a campaign contribution, even if you squint really hard when you read the definition. I also can't get worked up about "bank fraud", if the only fraud was not disclosing exactly how he would spend the loan on the application. Besides, it was an equity line of credit. I've got one. It would never occur to me to spend it on hush money to a sex worker, but I don't need to inform the bank about it.
On the other hand, no one gives away 130,000 dollars, ever. Michael Cohen claims that he took out a substantial loan, secured by his personal residence, in order to give money to Stephanie Clifford, so she wouldn't talk about having sex with Donald Trump, and he did it, .......just because. And Donald Trump knew nothing about it.
Somebody's lying. However, that's not a crime, so no one ought to have their home invaded or searched or anything like that, so where's the criminal element? Well, Michael Cohen clearly expected something in return for his 130k investment in Donald Trump's political future. Was that something that The Donald could only do for him after he was elected?
If so, that's bribery. This is a bribery investigation.
Time will tell whether the potential bribery is just a suspicion, or if they have reason to believe that some sort of quid pro quo existed that involved Donald Trump using presidential power. If such a quid pro quo exists, Mr. Trump can be, and ought to be, thrown out of office.
So far, it's speculation, but stay tuned.