Trump is now left, at least temporarily, without a traditional criminal defense attorney as Mueller’s team appears to be entering a critical phase in its investigation into Moscow’s interference in the 2016 election and whether the president’s campaign cooperated with Russia in this effort.
The official story is that both diGenova (who has gone on Fox News to defend Trump) and his wife, also an attorney, had conflicts of interest that'd prevent their representing Trump. This isn't especially unusual in the legal profession, and apparently their firm also represents a former Trump spokesman who has been called as a witness by Robert Mueller.
The story also says that Trump based his decision on having seen diGenova on Fox News, and that he didn't know him personally. Apparently reality was unable to live up to the hype:
Trump’s issues with diGenova and Toensing went beyond their conflicts, said a person who spoke to the president recently. After meeting with the husband-and-wife team on Thursday — after diGenova’s hiring had been announced — the person said Trump was less impressed with diGenova than he had been while watching the former U.S. attorney on television.
Apparently the Trump legal team is not the place to be. Ted Olson, one of the most famous lawyers in the country right now, recently turned down an offer to head up Trump's legal team. That's a pretty big deal, given that it would ordinarily be quite prestigious.
A number of white-collar attorneys in Washington said the president has been unable to attract top-flight talent as he looks to overhaul his legal team, with major firms fearful that an affiliation with Trump and the Russia case could impact their ability to attract other clients and hire new lawyers.