On a brisk Friday evening earlier this month, David Sacks and Elon Musk convened a dozen or so of America’s most powerful business leaders for dinner at Sacks’ $23 million, 11,000-square-foot home in the Hollywood Hills. The dinner party, according to people familiar with the intimate gathering, comprised a veritable living room Milken conference: Michael Milken himself was there, in fact, as were billionaires Rupert Murdoch and Peter Thiel. A few government types, including Steven Mnuchin, scored invites. There were also some less politically active titans of industry, such as Uber co-founder and former C.E.O. Travis Kalanick. But all were there as members of a burgeoning anti-Biden brain trust, united by a shared sense of grievance.