The author presents the Senates motivation as follows: they are jealous and/or fearful of Caesar's political clout and proven effectiveness as a military commander.

Does Goldsworthy really say this? I can't say I paid much attention to Goldsworthy when I read it, as his grasp of political and social history is really very poor. Goldsworthy's a marvelous military historian (his analysis of Caesar's campaigns is incredible, and his work on the Roman military is easily the most complete treatment of the subject in decades), but when he talks about politics or Roman society its a bit...stunted. By which I mean Goldsworthy clings to arguments that were discarded a long time ago (like...in the early 50s sometimes). This business about the senate being fine with Caesar until he goes off to Gaul, and trying to recall him because they were jealous is Mommsen's nonsense.

Senatorial opposition to Caesar began literally from the beginning of his career. In his youth Caesar was hunted by Sullan partisans, and when he returned from his military tribunate in Asia he was still being opposed simply for his connections with the Marians. Caesar's support of Pompey shows how at odds he was with much of the senatorial class--contrary to what Goldsworthy seems to imply, Caesar was far from the only politician hated by the senate (more on this later). Caesar's entire career was spent trying to pass legislation that people like Cato were vehemently opposed to, whether it was his own legislation or Pompey's. Many members of the senatorial class disliked and feared him long before he got to Gaul.

Caesar's recall from Gaul (or attempted recall) was a move by Cato to get back at Caesar, not for actions undertaken during his proconsulship, but during his consulship in 59. Caesar's consulship was massively important. During 59, Caesar essentially commanded as sole consul, having driven his colleague Bibulus to retire to his home for the whole year, and the legislation that Caesar was able to force through was nothing short of incredible. Most importantly Caesar got Pompey's Eastern Settlement passed and provided Pompey with his land distributions in the form of the decemvirate, both pieces of legislation that had been opposed since Pompey got back from Asia. Furthermore, much of Caesar's legislation was passed either illegally or by bypassing normal means, for which Cato wanted to make Caesar pay. Indeed, the senate started as soon as Caesar no longer had power over them. The consuls had no authority during the allotment of promagisterial commands, and Cato and his goons tried to stick Caesar with a proconsular command over the trees of Italy, instead of giving him a governorship (and the imperium that came with it). Caesar only got his governorship because during his consulship he had made good on his promises to Crassus and Pompey, passing their legislation, and so he was able to get their support in overturning Cato's decision.

That the senate might have feared Caesar as a general before fearing him as a statesman is pure fantasy. Caesar had long represented a direct threat to those in Cato's camp, and his use of tribunate power and political alliance (as well as coercion) to force legislation and judicial decisions through wasn't exactly looked on fondly by people like Cicero, who was no fan of Cato's. Likewise fantastic is the idea that if the senate feared Caesar as a general before a statesman, they feared him before all other similarly successful generals. Nonsense. When Pompey came back from Asia he was ordered to disband his legions, for fear that he might march on Rome like Sulla. Pompey refused, and camped his men outside the city for several years until his land distributions were passed. Pompey's use of armed force was far more notable than Caesar's ever was--several times Pompey threatened armed force or actually used it in the city. And Pompey was a perfectly skilled politician--Pompey got to the consulship extraordinarily quickly, by bypassing normal magisterial sequence (I vaguely remember that Goldsworthy thinks Caesar was something of a radical in the way he climbed through the ranks--this is nonsense, Caesar worked his way up through the cursus honorum like everyone else, it was Pompey who did it weirdly). Pompey had received much the same treatment before his agreement with Caesar--the senate blocked both the Eastern Settlement and the land distributions for a decade, and subjected Crassus to similar treatment.

But by 50, Pompey had swung back into the senatorial camp, despite being one of the most (probably the most) radical politicians in contemporary Roman politics following his first consulship with Crassus. The reasons for this are complicated. They include Clodius' threat of assassination (which was a big deal that I won't get into), his decision to recall Cicero (despite the fact that he had exiled him in the first place--Pompey needed to turn Cicero loose against Clodius), Julia's death, Crassus' death, and probably Caesar's Gallic success as well. Certainly by the time he marched his legions into the city to put down the riots after Clodius' murder Pompey was in the senatorial camp, though even at Pharsalus he didn't really side with Cato. The senate's dislike of Caesar and Cato's obsession with him all came from Caesar's consulship--Caesar's actions in Gaul were just an easy thing to latch onto for a prosecution (despite the fact that, arguably, he hadn't really done anything wrong in Gaul--Cato was largely using it as an excuse to attack Caesar's consulship)

If you want to really understand the political situation, don't read Goldsworthy. Read Gelzer