Prior to 1970, a Mob boss (not just a Don, but anyone who gave orders instead of carrying them out) could avoid prison through caution. If he lived modestly, laundered his money carefully, declared income from a "legitimate" job and paid taxes on that income, gave orders to subordinates one at a time without witnesses present, and was careful not to speak on the phone or in places that could be bugged, he had little to fear from the authorities. But in 1970, Congress passed the Racketeer Influenced Corrupt Organization (RICO) Act, which made it a felony, punishable by double-digit sentences, to conspire to be part of, or lead, a "criminal enterprise." "Conspiracy" is critical because, in most US courts, a felony conviction requires a "corroborating witness"--someone who'll back up the main witness against the defendant. And, as we know, witnesses against Mob bosses were few and far between. A conspiracy case doesn't require a corroborating witness.
What's more, even victims of the Mob can be prosecuted under RICO. A loan-shark victim, for example, who was forced to hand over his business to the Mob for unpaid debts and run it or "bust it out" for them, could be charged under RICO. This vastly increased the number of people who were willing to testify against mobsters in return for reduced charges.
Four NYC Mob bosses were indicted on RICO charges (the fifth, Vincent "Chin" Gigante, was declared non compos mentis-- mentally unfit to stand trial at that time). They were nailed by a combination of wiretaps and other electronic surveillance, and witnesses. Three went to prison for 90 years or more. Paul Castellano was whacked before he went to trial. John Gotti, who was not yet head of the Gambinos, was due to go on trial under RICO with his then-boss Aniello "Mr. Neil" Dellacroce, but Mr. Neil died on the day the trial was to begin, and the government took many months to separate out Gotti's case from Mr. Neil's. Gotti was eventually acquitted on the RICO charge, but as you know, he was nailed for Castellano's murder and died in prison last year.