That's not a good look at all for a corporate M&A attorney. His clients are going to generally be large corporations, headed by people who are more likely to vote Republican. There are plenty of good big firms out there other than Sullivan & Cromwell, and a lot of good Sullivan & Cromwell M&A guys other than this clown. It's likely many of them didn't know his politics, but they will now.
All it takes for a few large clients to get pissed at this, and he may lose an awful lot of money.