Troy Jackson has further tightened his grip on Maine’s Democratic nomination for Senate.

Mr. Jackson, a logger and former state lawmaker, is set to appear on the ballot at Democrats’ nominating convention on Saturday in Bangor alongside just two other candidates who have won almost no public support from delegates: David Costello and Saundra Pelletier.

Hundreds of delegates aligned with Mr. Jackson were elected last weekend, giving him a seemingly insurmountable advantage that forced his leading primary rivals to suspend their campaigns.

The lack of well-known opponents appears to set up the convention as a celebration of Mr. Jackson’s nomination. His campaign announced on Monday that it was turning its effort toward defeating Senator Susan Collins, a five-term Republican, in a race widely seen as crucial to control of the Senate.

While the other top contenders had announced that they were withdrawing from the race, there had been indications that at least one of them hoped to appear on the ballot at the convention.

But when the state party announced on Tuesday which candidates had made the ballot, the other leading candidates were not included — meaning that they had not turned in the 500 verified signatures required for a spot.

They included Dr. Nirav Shah, a former public health official who came in second in the primary for governor in June; Shenna Bellows, the Maine secretary of state, who came in fourth in that race; and Jordan Wood, a progressive activist who placed third in the Democratic primary for Maine’s Second Congressional District. Dr. Shah had previously announced that he had gathered more than 800 signatures.

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