Sean O’Brien was a rising star in the International Brotherhood of Teamsters in 2017 when the union’s longtime president, James P. Hoffa, effectively cast him aside.But that move appears to have set Mr. O’Brien, a fourth-generation Teamster and head of a Boston local, on a course to succeed Mr. Hoffa as the union’s president and one of the most powerful labor leaders in the country.A Teamsters vice president who urged a more assertive stand toward employers like the United Parcel Service — as well as an aggressive drive to organize workers at Amazon — Mr. O’Brien has declared victory in his bid to lead the nearly 1.4 million-member union.According to a tally reported late Thursday on an election supervisor’s website, he won ab …
