Republican state Sen. Dean Tran, left, and Democratic challenger John Cronin.

DEMOCRAT JOHN CRONIN was clinging to a tiny lead over Republican Sen. Dean Tran of Fitchburg early Wednesday morning, but Cronin said the trendlines were enough for him to declare victory.

“We are confident based on the current tally and outstanding numbers to declare victory,” said Cronin. Tran did not concede and the Associated Press hadn’t called the race for either candidate. As of 12:30 a.m., Cronin was leading 51-49 with 72 percent of precincts reporting. Results from Fitchburg, Tran’s hometown, were not available.

If Tran were to lose, the number of Republicans in the 40-member Senate would drop from four to three.

Cronin, a military veteran and political newcomer from Lunenburg, focused his campaign on the Senate’s vote in March to discipline Tran for using his State House staff to do campaign work. The Senate stripped Tran of his leadership position, removed him from his office, and required him to communicate with staff by email only.

Tran said his fellow senators relied on false information supplied by his political opponents and insisted he “did not do anything intentionally wrong with respect to my staff and volunteers on my campaign.”

In the seven other races at play in the Senate, the Democratic or Republican incumbents either won their races or were leading as of early this morning.

The three other Republicans in the Senate will be returning to the chamber next year. Sen. Patrick O’Connor of Weymouth defeated Democrat Meg Wheeler of Cohasset (Wheeler conceded) and Sen. Ryan Fattman of Worcester downed Democrat Christine Cream of Milford. Sen. Bruce Tarr of Gloucester ran unopposed.

The Democratic senators facing challengers also appeared to prevail. Sen. Becca Rausch of Needham was leading Republican Matthew Kelly of Franklin, Sen. John Velis of Westfield beat Republican John Cain of Southwick, and Sen. Anne Gobi of Spencer was ahead of Republican Steven Hall of Sturbridge by five points with 55 percent of precincts reporting.

In the other Senate races where incumbents faced challengers, Sen. John Keenan of Quincy beat Independent Alexander Mendez and Sen. Susan Moran of Falmouth was leading Republican James McMahon, whom she defeated earlier this year in a special election.

Bruce Mohl oversees the production of content and edits reports, along with carrying out his own reporting with a particular focus on transportation, energy, and climate issues. He previously worked...