You're right: Rosselli had huge connections, going back to his early days in New York and Chicago. When he came to LA in '24, he was essentially a free agent, but a known friend to Capone. He worked for Tony "The Hat" Cornero early on in his bootlegging operations, and later for Jack Dragna, who ran the weak LA Mafia. Rosselli rose quickly, and became the smooth-talking gambler/wheeler-dealer that partied with many of the Hollywood stars and movie moguls. It was during this time that he befriended Joe Kennedy, who he would remain close to (in a very careful fashion) until Joe's stroke in Dec. '61 (a very critical moment in our nation's history, when Joe's Machiavelian maneuvers suddenly spun out of control).

Rosselli became known for his ability to show how everyone could win, without violence. He smoothed the transition of Ben Siegel into the LA mob scene, including keeping the feisty ex-boxer, Mickey Cohen, from upsetting the apple cart. Guys in NY like Frank Costello and Meyer Lansky got good reports on Johnny from Ben, and his stature rose.

Rosselli's involvement in the big IATSE case gave him national exposure in the '30s and early '40s with the NY mob and his old friends in Chicago. And, he became acknowledged as a "stand up guy" for keeping quiet when he and several of the Chicago bosses, including Rosselli's close friend and mentor, Paul Ricca, were convicted in the labor racketeering case.

When Rosselli got out, he returned to LA, and continued to bolster his power base, despite the fact that we wasn't a boss. The LA Mob was becoming an embarrassment, and when Rosselli was passed over after Dragna's death, he was happy to get out of LA. He went to Havana and worked at the San Souci (Trafficante's place), but was known to be close to Meyer Lansky, and reportedly became an intermediary between Lansky and Batista.

Everything I've read indicates that all went well for Rosselli in Havana, and his stature rose. That was when he was tapped to take over as the "Man" without a crew in Vegas. He was there because he was trusted to be a fair arbiter of the various mob interests in the open city. His first project was to demonstrate that everyone, working together, could make money and keep the blood from flowing. The Tropicana brought together mob families from NY, New Orleans, and Chicago, and it's been reported that even that old gangster, Joe Kennedy, had a piece of the Trop.

It's no surprise that Rosselli presided over the "Golden Age" of Vegas, where style was required, and violence was forbidden under the "Pax Rosselli." This position only strengthened his growing reputation among the power elite. Whether it was Howard Hughes, the Kennedys, or the bosses at the top of the Commission, people listened to Rosselli... for a reason.