We all know Binks was banished from Otoh Gunga, but before that he was sentenced to hard labor for another crime. This is where his corruption began; he began to hate the Gungans and Naboo, and after he was released, he vowed revenge on them all. Sometime after this, he was banished for being "clumsy". What actually happened is that he "accidentally" caused a huge explosion at a political gathering with Boss Nass's home. Clearly this was an attempt to assassinate the leader of the Gungans.
So when the Separatists invaded Naboo, he clearly saw this as his opportunity. He distracted the Jedi, whom he knew would be a major threat to the Separatists. Here's a list of other stuff he did throughout the films:
-Tried to get the Jedi arrested by overtly stealing from a merchant
-Attempted to sabotage Anakin's podracer by reaching into the engine to disable it
-Again attempted to sabotage his podracer by dropping a wrench into the engine minutes before the race started
-Managed to get himself into a position of power by negotiating a deal between the Gungans and Naboo, which led to his promotion to general of the Gungan army (it's likely he thought the droids would massacre both armies, and didn't expect the allies to win)
-Tried to sabotage the Gungans by letting a bunch of their blue balls fall out of a truck
-Surrendered the Gungan army
Here's the big one:
-When Padme was on Naboo due to the attempt on her life, she asked Jar Jar to stand in for her. He used this opportunity to directly defy her wishes and [u]convinced the senate to give Palpatine "emergency powers" to create an army for the republic. Jar Jar was effectively the cause of the Clone Wars. When Palpatine became the emperor, he was considered an ally of the Empire.[/u]
Sometime between Episode 1 and 2, Palpatine must have gotten to Jar Jar. We see in Episode 1 that he acts solely to get revenge on the people of Naboo, but in episode 2 he ramps up his evil actions to help Palpatine rise to power. I think Palpy noticed Jar Jar's sabotage during the Battle of Naboo, and because of their closeness (they were both politicians from Naboo), he corrupted him over time, possibly teaching him about the Sith and his plans for an Empire.
The answer is obvious. Jar Jar was a Sith agent that is personally responsible for everything bad that happened in the Star Wars series.
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It's worth noting that he later impersonated the King of the Gungans, perhaps in some attempt at revenge to bring the society that shunned him down. He's a psychopathic maniac who must be stopped.