WASHINGTON  In the days leading up to the Delaware primary, Sal Russo hosted a radio fund-raiser, organized a political rally and pressed the case with reporters that Christine O’Donnell was the Tea Party’s choice for the United States Senate. He also set off what he calls a “money bomb,” pouring at least $250,000 into television and other advertisements promoting the little-known candidate.

With Ms. O’Donnell’s upset victory in the Republican primary on Tuesday, Mr. Russo, the chief strategist behind an upstart group called the Tea Party Express, had racked up another win.

But in becoming one of the movement’s most successful players by helping Tea Party favorites oust incumbents or trounce rivals in four states, Mr. Russo is also fast becoming among the most divisive.

Unlike many of the newly energized outsiders who have embraced Tea Party ideals, Mr. Russo, 63, is a longtime Republican operative who got his start as an aide to Ronald Reagan and later raised money and managed media strategy for a string of other politicians, including former Gov. George E. Pataki of New York. His history and spending practices have prompted some former employees and other Tea Party activists to question whether he is committed to, or merely exploiting, their cause.