Vice President-elect Kamala Harris Resigns Her Senate Seat

A senator resigns to prepare for a new role in a Senate with a 50-50 split. Due to the Georgia Runoffs, Vice President Elect Harris will cast tie-breaking votes. In a Medium post, she expressed a preference for the Senate to find common ground rather than relying on her to break ties.

What role is the new senator preparing to take on?

What was the context of the message posted on Medium?