Scipio's not exactly the only Roman aristocrat to be prosecuted following great service to the state. Actually, it's kind of common. The Roman aristocracy relied on the individual magistrate or promagistrate to get anything done, but was highly suspicious of the individual standing head-and-shoulders above his peers. The individual of unusual dignitas and auctoritas through his actions was expected to retire from public duties, or voluntarily accept an advisory role for the next generation. This of course did not happen in practice often, even in Scipio's lifetime. Scipio was the political enemy of Marcus Cato, who constantly opposed him at the end of his life, with his characteristic persistence. Part of this was because the nobility, suspicious as usual, did not look kindly on his enormous prestige. Scipio really did have extraordinary dignitas following Zama--there built up around him soon after the "Scipionic Legend," in which Scipio was said to have performed various miraculous deeds and to have been the son of a god (usually Jupiter). For example, Livy says that there was a story that Scipio was conceived when his mother was visited by a giant snake--Livy thinks the story is ridiculous, and points out that it was already being told of Alexander, but certainly that gives an idea of the sort of legend that was built up around Scipio within only a short time. Besides the rather unwelcome influence of the growing Scipionic Legend the senatorial class did in fact have some reason to feel insecure about Scipio. Scipio's later career was relatively unremarkable, but not really for want of trying. He held the censorship in 199 and was princeps senatus twice in 194 and 189, both somewhat expected of a consular, though Scipio wasn't exactly an ordinary consular. Scipio was, however, consul for a second time in 194, and lobbied for the right to command the war against Antiochus III, a motion which was knocked down in the senate. Scipio did not fight at Magnesia, but he volunteered against Antiochus as legate under his brother in 190. It's not hard to see why Scipio, the quite literally legendary victor over Hannibal and recent consul for the second time, might be suspected by the senatorial class of really being the one pulling the strings in the war, especially when it was Scipio who arranged the peace with Antiochus. Certainly the senatorial class was uncomfortable with the freedom with which Scipio threw his reputation around, and they were not totally unjustified, as Scipio's behavior was not very in character with the expectations of a member of the senatorial class. Following his return from the war against Antiochus Scipio (and his brother) were both attacked by Marcus Cato in the courts--clearly the conduct of this war, and the suspicions of misconduct during it, were the last straw, so to speak.