The Service Employees International Union gave Barack Obama its highly prized endorsement on Friday afternoon. The S.E.I.U.Â’s endorsement is especially coveted because the union has 1.9 million members and has a rank-and-file that is far more politically active than most other unionsÂ’. Moreover, its political action committee is expected to collect more than $30 million this campaign, making it one of the biggest PACs in the nation.