Sen. Bernie Sanders (I-Vt.) on Thursday suggested Democratic Maine Gov. Janet Mills should reconsider her imminent plans to announce a Senate bid — to avoid "wasting millions on an unnecessary … divisive primary."

• Instead, Sanders urged Democrats to coalesce around progressive Graham Platner, a rising star on the party's left.

Why it matters: Democrats are barreling toward an explosive primary in Maine, which is shaping up to be a high-profile showdown between the party's leadership and its left flank.

• "Graham Platner is a great working class candidate for Senate in Maine who will defeat Susan Collins," Sanders posted on X on Thursday. "We need to focus on winning that seat and not waste millions on an unnecessary and divisive primary."
• Mills plans to announce her Senate bid as soon as next week, Axios scooped earlier this week.
• But Platner, who launched his campaign over the summer and has raised over $3 million, has built grassroots momentum with Sanders' backing.

What they're saying: "It's disappointing that some Democratic leaders are urging Governor Mills to run," Sanders said on X.

• Senate Minority Leader Chuck Schumer (D-N.Y.) has encouraged Mills to run for the chamber for months. Her statewide name recognition and two gubernatorial victories make hers an attractive resume for party leaders.
• Two other Democrats are also in the race: Dan Kleban, the owner of the Maine Beer company, and Jordan Wood, a former congressional staffer.
• Democrats are trying to knock off longtime Sen. Susan Collins (R-Maine) next year, their top target on the Senate map.