This article is pretty good, too:
'The result is that Trump is trying to use his divorce attorney Marc
Kasowitz to represent him in a counterintelligence investigation that
has the highest political stakes. And that’s an eighth reason why the
big firms won’t touch the case. Mike Allen explains:
...
He’s stuck with a guy who specializes in pre-nuptial agreements and who
represented him in his Trump University fraud cases.
"The president’s chief lawyer now in charge of the case is Marc E.
Kasowitz, a tough New York civil litigator who for years has
aggressively represented Trump in multiple business and public relations
disputes — often with threats of countersuits and menacing public
statements — but who has little experience dealing with complex
congressional and Justice Department investigations that are inevitably
influenced by media coverage and public opinion."'
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http://washingtonmonthly.com/2017/06/06/why-no-lawyers-will-represent-trump/>