While the story is being reported as centered on Cohen's role as fixer for President Dennison's sexual escapades, this looks to me like a gold mine for the core collusion questions. Cohen has been central to Dennison's Russian / Mafia connections for decades. Check out the new Rolling Stone piece dealing with Cohen's long history of serving Russian oligarchs by laundering their money through his taxi businesses and connecting them to Trump properties where they buy a large percentage of available condos....often through opaque LLCs.

When Mueller tells his full story about Dennison's crimes, it will start with financial transactions made years ago with these same Russian Mafiosi. He has been a Putin project since he burned all of his legitimate financing options.

Cohen and Felix Sater were the facilitators.

If they can promise Cohen decades in prison for his financial mis-deeds, Mueller may be able to use his testimony to seal the deal for indictments and impeachment over treason charges.

And Sater apparently unloaded a tranche of info to Mueller and that will probably force Cohen to unload a good chunk of the rest.
https://www.buzzfeed.com/anthonycormier/felix-sater-trump-russia-undercover-us-spy?utm_term=.bhrNlgmQmb#.xsZn385W5a

I saw him on do a Chris Hayes interview last month and the man is smooth mafioso.

It appears Mueller is also gathering all sorts of ancillary stuff related to Cohen in order to force him to do a huge plea deal.