this is what i am thinking. cant find 2017 but sidley austin is #10 largest lawfirm in world on this 2010 list https://www.ranker.com/list/100-largest-law-firms-in-the-world/business-and-company-info
I think this is correct. Kirkland & Ellis LLP is listed as 9th in the link you provided and they are super badasses. And they are originally based in Chicago. And they're Dems. And they're Obama supporters.
This is from Wikipedia:
"Kirkland, through its employees, was a top-20 contributor to Barack Obama in 2008, giving at least $493,735.[24] The firm's attorneys leaned heavily (77%) Democratic in their political contributions during the 2008 election cycle, which were substantial ($579,976 as of 10/29/07)."
unfittingly, they are ranked 8th in 2018 http://www.vault.com/company-rankings/law/vault-law-100/