PIERRE, S.D. (AP) — For the homestretch of a suddenly competitive four-way Senate race here — one that could tip control of the Senate — former Sen. Larry Pressler is bringing in the best surrogate he can imagine: a 78-year-old retired FBI agent. With him will be retired agent John Good, who led the FBI sting in the Abscam bribery scandal in the late '70s, which led to 19 convictions, including six House members and one senator. [...] Democrats and Republicans agree, he has disrupted an otherwise uncompetitive Senate race that Republicans are counting on in their push for a Senate majority. Pressler is a key player in a fluid race with former Gov.