Overview

• Mills, 77, formally entered the race with a video centered on her clash with President Donald Trump over transgender-athlete policy and a funding freeze that courts and the administration ultimately reversed.
• She joins a competitive Democratic primary featuring Graham Platner, Jordan Wood and Dan Kleban, with Platner backed by Sen. Bernie Sanders and planning to continue his insurgent campaign.
• Sanders urged Mills not to run, warning against an expensive, divisive primary as progressives press a case for generational change within the party.
• Collins, 72, is widely expected to seek a sixth term and remains a formidable incumbent; election handicappers currently rate the race Tilt Republican.
• Mills told the Boston Globe she would serve only one term if elected, as national Republicans immediately targeted her age and record with new attacks.