Maine Democrats will hold a convention on July 25 where they will select a new Senate nominee to replace Graham Platner, Charles F. Dingman, chair of the state party, said Friday.
The convention will be held at the Cross Insurance Center, a small arena in Bangor, Maine, according to rules released by the state party.
Maine Democrats are planning to hold county meetings to choose delegates next weekend and the state convention the weekend after that to pick a replacement for Mr. Platner, who filed paperwork to end his campaign on Friday. He had faced widespread pressure from party leaders and allies to bow out after a rape allegation, which he denies.
Officials in the state are trying to create a process to choose a Platner replacement by a July 27 deadline, a herculean task for a small state party.
“I have issued the call for a nomination convention to choose a new nominee for U.S. Senate,” Mr. Dingman said in a video statement released by the state party Friday night. “This call to convention provides the most inclusive, representative and transparent process possible under these unprecedented circumstances and the applicable laws.”
Since Mr. Platner’s announcement on Wednesday that he would suspend his campaign, Maine Democrats had discussed an array of possibilities of how to choose several hundred party delegates to vote on his replacement.
The process is riddled with political hazards.
During a Thursday night meeting of the state’s 16 county Democratic Party leaders, officials discussed methods for choosing delegates to the state convention, according to two people familiar with the emerging plans, who spoke on the condition of anonymity to discuss private talks.
One logistically challenging option that was under consideration would have each county party hold meetings to vote on whom to send to the state convention. This would put a premium on organization from each of the state’s new Senate campaigns and could lead to many hours of speeches and voting in each county.
An arbitrary procedure that has been discussed would be to hold a random draw of attendees at each county gathering — in effect, picking names out of a hat from among those who show up. But it was not clear how much appetite there would be for such a process.
One Democratic county chairman, Bruce Bryant of Oxford County in western Maine, wrote on Facebook that his county party would hold a gathering on July 19 to determine its delegates.
With a little over two weeks to replace Mr. Platner and a tiny state party staff — the Maine Democratic Party touts on its website that it increased its employee head count to 18 from four in 2025 — Democratic officials from around the country are beginning to converge on Maine to assist. About 10 state Democratic parties have sent or are sending staff members to Maine to help with logistics and public relations.
One outsider who has taken on a senior role in organizing the caucus process is Troy Price, the executive director of the Association of State Democratic Parties, according to three of the people involved with the emerging plans. Mr. Price has worked in senior positions in state Democratic parties in New Hampshire and Iowa, where he oversaw the disastrous 2020 presidential caucus. Mr. Price did not respond to messages on Friday.
Whoever is chosen as the new nominee will face Senator Susan Collins, a five-term Republican who has defied political gravity in the past and defeated an array of Democratic challengers. Ms. Collins is the only Senate Republican facing re-election this year in a state President Trump lost in 2024.
Democrats must flip at least four Republican-held Senate seats in this year’s midterm elections to take a majority in the chamber. The Maine seat has long been viewed as their best opportunity to seize a G.O.P. seat.
A number of Maine Democrats who lost in recent high-profile primaries have piled into the nominating contest.
They include Nirav Shah, a former public health official; Troy Jackson, a former president of the Maine Senate; Shenna Bellows, the Maine secretary of state; Jordan Wood, a former congressional staff member; Dan Kleban, a founder of a brewery; and Paige Loud, a social worker.
Mr. Shah, Mr. Jackson and Ms. Bellows all ran for governor and lost in the primary last month. Mr. Wood and Ms. Loud lost in the House primary in northern Maine’s swing congressional district. Mr. Kleban is relatively new to politics but briefly joined the Democratic Senate primary race last year before dropping out.
Under rules set by the state party this week, candidates must secure 500 signatures — including 50 from eight different counties — by July 21 to be eligible for the nomination. They must declare their intention to seek the nomination by next Wednesday. And they must submit brief statements describing “how their campaign will continue to support and build on the currently existing grass-roots energy and movement in Maine.”
Mr. Platner officially withdrew his candidacy on Friday, sending a letter to the Maine secretary of state. “Please consider this notice as my official withdrawal from consideration for this office,” he wrote. Mr. Platner’s departure was confirmed by Jana Spaulding, an aide to the Maine secretary of state.
Patricia Mazzei contributed reporting.