I don't think this is necessarily true. Bernie Sanders and Angus King are both independents. In the last 2 years, Democrats have held only 48 seats strictly speaking...they never had the majority. Kyrsten could have been an independent and caucused with the Democrats just as they do, all along. But Kyrsten is about Kyrsten. She had more power & visibility as a holdout Democrat. Now she wouldn't (because Bernie and Angus are far more reliable votes, and less self-absorbed). So to make things about her, again, she moves independent to stay relevant, because god forbid people stop talking about her. I don't actually think she does this stuff for power necessarily (lets be honest, she isn't going higher than the Senate), but to feed her craven need for attention.