In his book I Heard You Paint Houses about the career of Delaware-born mob hitman Frank Sheeran, author Charles Brandt answers that question by drawing a makes a fleeting reference to the local Wilmington mob, a branch of the Philly mob family.
I can t remember the details but if I can find that reference I'll post it.
This is a great article--a truly seminal work on Joe Biden worth continued scrutiny. It's all there, back in 1974.
...and here's the answer from the Labor Union Report:
Reportedly, it was the Teamsters—or, more accurately, a mafia hitman named Frank Sheeran who also happened to be the president of Teamsters local 326 in Delaware—who helped make Joe Biden a U.S. senator.
“In the fascinating biography of Teamsters and Mafia hit-man Frank Sheeran, “I Heard You Paint Houses,” the lifelong thug describes a favor he performed while he was president of Teamsters Local 326 in Wilmington, Delaware.”
“In 1972 Sheeran received a visit from ‘a very prominent lawyer’ he knew who was “very big in the Democratic Party” in Delaware. The November general election was approaching, and the race for the U.S. Senate seat held by a Republican was expected to be close. The lawyer wanted help in preventing the distribution of a paid Republican political ad – an insert in the Delaware-wide newspapers – that would run for a week and expose the campaign misrepresentations by the Democratic challenger. Sheeran promised the operative that he ‘would hire some people and put them on the picket line.’ He added, ‘People nobody would mess with.'”
“The picket line went up, the papers were not delivered all week, and, as Sheeran said, ‘The day after the election the informational picket line came down, and the newspaper went back to normal and Delaware had a new United States Senator.’ His name was Joe Biden. Thereafter, said admitted extortionist, thief and murderer Sheeran, of Biden, ‘You could reach out for him, and he would listen.'”
Once the mob does you a favor, you're beholden to them.