system
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human
[Star Wars] Why didn't Palpatine eliminate Mon Mothma?

Bail Organa and Mon Mothma were leading figures in the Rebel Alliance, effectively forging the movement from the rebel cells scattered across the Galaxy. They helped train and inspire other leaders such as Leia. Although Bail himself died before the Rebellion came into full swing, Mothma would continue the movement, becoming the leader of the Alliance and then Chancellor of the New Republic. **Mon Mothma probably did more to topple Palpatine than any Jedi Master could have.** The Emperor should've done something before she ran off and raised a rebellion.

Even before the rise of the Empire, Mothma and Organa were big obstacles in Palpatine rise to power, what with their objections to increased executive power, increased military spending, and attempts to sue for peace with the CIS. Not to mention Organa competing for the Chancellorship after Valorum stepped down.

Why didn't Palpatine get any Dark Side visions telling him that he needed to eliminate Mothma and Organa? Why did he allow them to remain in the Senate and influence public opinion? If he did decide to eliminate them, would the Rebellion ever become a big enough threat to defeat him? How does the saga play out?
gpt
Simply put, he did not know that they were providing material support to the Rebellion. They did a fairly good job of covering their tracks for a long time. Before Mon Mothma was branded a traitor for speaking out in 2BBY, she was probably seen as a harmless voice of dissent to give the illusion that the Senate could provide a meaningful check on his rule. After all, needlessly silencing people would only server to further inflame the public and feed the Rebellion with easy PR. 

Bail Organa maintained his cover all the way up to ANH when Princess Leia was captured following the Battle of Scarif, thus providing direct evidence of House Organa's material support to the Rebellion and providing the Emperor with the excuse necessary to "temporarily" suspend the Senate and also lead to the destruction of Alderaan. 

As for how he didn't know they were supporting the Rebellion, he just simply didn't know. Palpatine was not omniscient, no matter how strong in the Force he was.