timelets

But the Southern District can investigate any aspect of Trump’s behavior that took place in its jurisdiction, at any time.

And unlike Mueller, who could in principle be fired, the Southern District isn’t one man; it’s a whole office of career lawyers. It can’t be fired. Even if Robert Khuzami, the acting U.S. attorney in this case, were removed, no new U.S. attorney could realistically call off the prosecutors.
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The Southern District could explore money laundering crimes, tax evasion, or bribes of foreign officials or governments, which are illegal under the Foreign Corrupt Practices Act.
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Current Department of Justice guidelines say a sitting president can’t be indicted. But they don’t say anything about indicting the president’s business.

https://www.bloomberg.com/view/articles/2018-08-26/southern-district-of-new-york-will-tear-into-trump-organization

First, I wanted to write that this is a yet another reason for a businessman not to run for a high public office: the business becomes exposed to retaliation from political enemies. Then, I remembered that Michael Bloomberg was one of the most successful mayors of NYC, despite being a prominent businessman. Therefore, it's not about a businessman entering politics. Rather, it's about a particular notorious businessman doing a particular kind of shady business.