Question:
What specifically did Caesar think he would be charged with. Was it for killing the supposedly allied Germans, the one which Cato put a motion forward to turn him over to the Germans? Was it mismanagement of his province? Or was it just simply that he felt his rivals would trump up some charges on him?

Short Answer:

You mentioned Plutarch's versions of events. You can also check out

• Appian
• Cassius Dio
• Suetonius

Julius Caesar, Nephew to the Great Roman Politician / General Gaius_Marius was born to a noble Roman Family, but he did not have the kind of wealth which would permit him to succeed in Roman Politics and fulfill his ambitions. Worse, pursuing his political ambitions had left him in great debt. To these ends he pursued Governorships in Roman Provinces. The money to be made in Governing a Roman Province was in extortion and in military adventurism. Caesar did both and obtained great wealth as well as enjoying immunity from prosecution. Caesar invaded unstable regions boarding on the provinces he was governing. He used the spoils of these campaigns to build his legions and conduct more lucrative wars. He subdued Gaul and invaded both Germany and Britain successfully. All of this while common was technically illegal. Caesar though knew he would be prosecuted because he used his fame and fortune to curry political power in Rome. His rivals would use his path to wealth as a fulcrum to separate him from his political allies. The Senate aligned with Caesars chief rival Pompey used these illegalities in an attempt to check Caesar's popularity politically. The Senate, lead by Pompey declared Caesar an enemy of the Rome; and after that Caesar crossed the Rubicon and invaded Rome.

Detailed Answer:

When Caesar said this is their (the Senates) fault, If I had disbanded my armies they would have condemned me in court; he's referring to the cat and mouse game he was playing with the Senate and probable more importantly "Gnaeus Pompous Magnus", or **[Pompey the Great][2]**.

Like all great political intrigue, and Julius Caesar is considered one of histories greatest military and political leaders; there where wheels inside of wheels working to propel actions.

Background:

Julius Caesar, **[Marcus Licinius Crassus][4]**, and "Gnaeus Pompous Magnus" formed a military-political alliance known as the **[First Triumvirate][3]** around 60BC. Caesar was an up incoming politician from a noble Roman family. Crassus was the wealthiest man in Rome. Pompey was considered the greatest military leader at the time of this alliance. Having fought and won two great wars. Third Servile War (73–71 BC) and the Third Mithridatic War (73–63 BC). After Pompey's wife, Julius Caesars daughter, died 54BC the political alliance between Pompey and Caesar began to frey. Crassus died in a war with the Parthians in 53BC the Triumvirate was shattered.

You see, while Caesar was arguable a junior member of the Triumvirate while the Triumvirate was initially established; while the Triumvirate lasted, Caesar had made the most of his time. Caesar had conquered Gaul, and become a famous military leader, as well as exceedingly wealthy. Worst of all Caesar aligned himself with the plebiscite the common man, who were Pompey's base supporters. Caesar was eclipsing Pompey in wealth, military reputation, and politically. So that's the backdrop.

Answer:

What was occurring before and during Caesars decision to cross the Rubicon.

Pompey was looking to take Caesar down a peg or two. He wanted to weaken Caesar politically and militarily. To do this Pompey had to deny Caesar any subsequent governorships which would convey upon him further immunity from prosecution. Further, Pompey was trying to persuade Caesar to disband his legions and return to Rome. Pompey wanted to publicly humiliate Caesar, and perhaps banish him from Rome for a few years. Both of these steps would separate him from his military and political allies and make Pompey's Caesar problem much more manageable.

Caesar on the other hand was in an exceedingly strong position. His goals were to appear weak, invite / provoke Pompey and his allies to deny him a reasonable outcome; and generally appear to be a victim to Pompey and the Senate. So Caesar fed rumors that his legions were rebellious. That some of his legions basically only existed on paper they were so depleted by the Gaulic Wars and campaign illnesses. Finally, when he did approach Rome, Caesar did so with only one legion, the 13th legion.

You see, Caesar while a popular commander still commanded Roman soldiers. He knew he was in a strong position but he had to make it seem he was a reluctant invader. That Pompey's actions were not just against him, but also against his Legions.

So when the Senate declared Caesar an enemy of Rome, the Dye was cast, and Caesar obtained his justification for invading Rome. Impressively politically Caesar arguable could appear to be the victim, when in reality Caesar held all the cards.

Caesar's Civil War

In 52 BC, at the First Triumvirate's end, the Roman Senate supported Pompey as sole consul; meanwhile, Caesar had become a military hero and champion of the people. Knowing he hoped to become consul when his governorship expired, the Senate, politically fearful of him, ordered he resign command of his army. In December of 50 BC, Caesar wrote to the Senate agreeing to resign his military command if Pompey followed suit. Offended, the Senate demanded he immediately disband his army, or be declared an enemy of the people: an illegal political bill, for he was entitled to keep his army until his term expired.

A secondary reason for Caesar's immediate desire for another consulship was to delay the inevitable senatorial prosecutions awaiting him upon retirement as governor of Illyricum and Gaul. These potential prosecutions were based upon alleged irregularities that occurred in his consulship and war crimes committed in his Gallic campaigns. Moreover, Caesar loyalists, the tribunes Mark Antony and Quintus Cassius Longinus, vetoed the bill, and were quickly expelled from the Senate. They then joined Caesar, who had assembled his army, whom he asked for military support against the Senate; agreeing, his army called for action.

In 50 BC, at his Proconsular term's expiry, the Pompey-led Senate ordered Caesar's return to Rome and the disbanding of his army, and forbade his standing for election in absentia for a second consulship; because of that, Caesar thought he would be prosecuted and rendered politically marginal if he entered Rome without consular immunity or his army; to wit, Pompey accused him of insubordination and treason.