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Trump-backed Geoff Diehl will take on Democrat Maura Healey in Massachusetts governor's race, CNN projects

(CNN) Geoff Diehl, a former state lawmaker endorsed by ex-President Donald Trump, will win the Republican nomination for Massachusetts governor, CNN projects, setting up a showdown with Democratic state Attorney General Maura Healey.

Republican Gov. Charlie Baker's decision not to seek reelection this year upended the Bay State political world, setting off a scramble among ambitious members of both parties as the top job -- which Baker had won twice -- suddenly came open and set off a domino effect down the ballot.

Despite its liberal reputation, Massachusetts has a long habit of electing Republican governors -- Deval Patrick, who served two terms, is the only Democrat to hold the corner office on Beacon Hill since Michael Dukakis left it in 1991 -- and Baker, even in this era of sharp partisan divisions, routinely polled as one of the country's most popular state leaders.

His departure, in the face of intraparty opposition to his criticism of Trump and the prospect of a primary challenge, paved the way for Diehl to claim front-runner status for the GOP nomination. Diehl will defeat businessman Chris Doughty, who, despite being complimentary of the former President, had argued that his political brand is toxic in Massachusetts and a statewide candidate like Diehl would be doomed to defeat in the general election.

In his endorsement of Diehl last year, Trump mostly railed against Baker -- who had not yet announced he wouldn't run again -- denouncing the governor as a "RINO," or Republican in Name Only, and saying his climate policy views were "fresh out of the AOC playbook," a reference to progressive New York Rep. Alexandria Ocasio-Cortez.

"Geoff Diehl, on the other hand, is a true patriot, a believer in low energy costs and our independent energy policy," Trump said.

Diehl will be the heavy underdog in the general election against Healey, whom CNN projected earlier Tuesday would win the Democratic nomination, setting her up to potentially become the state's first out lesbian governor. Healey, after months of weighing her options, jumped into the open-seat race less than two months after Baker bowed out.

Massachusetts Attorney General Maura Healey addresses the audience at a watch party on Tuesday in Boston.

Healey's announcement, in late January, cleared the field of previously declared Democratic candidates. Her fundraising prowess and national stature, sharpened during Trump's presidency when she often challenged his administration in court, has made her a household name among commonwealth Democrats who believed she represented the party's best chance to unseat Baker.

In addition to the top of the Democratic ticket, the party's congressional delegation is all but settled following recent cycles of upheaval. None of the nine members of Massachusetts' all-Democratic US House delegation are facing a primary challenger this year.

So, much of the intrigue Tuesday came from a pair of primaries that might not have been close -- or even contested, in one case -- had Baker sought a third term.

On the Republican side, Diehl emerged from a contentious contest with Doughty, who had argued that he represented the GOP's best chance to defeat Healey in November. (Diehl had the state party's endorsement, but Doughty secured enough delegates at its May convention to make the ballot.)

Doughty -- who has said he voted for Hillary Clinton in 2016 and Trump in 2020 -- got a late boost from influential conservative radio host Howie Carr, who, echoing the candidate's electability argument, backed Doughty over Diehl.

Meanwhile, Diehl and Leah Allen, his allied candidate for lieutenant governor, held a tele-rally with Trump on Monday evening.

The Boston Globe editorial board, though far from an influential voice with Republican primary voters, beseeched them (and eligible independents) to choose Doughty and begin a "party reset."

"That process will take years, but voters can jump-start it by choosing Doughty, a calm voice for a more pragmatic conservatism, over Diehl, a dedicated acolyte of former President Donald Trump," the board wrote.

Diehl refused a televised debate with Doughty (they debated on Carr's radio show back in July), so WBZ in Boston last week held a "virtual debate" -- conducting separate interviews, back-to-back, then editing parts of them together.

"He's too extreme for our state, he pursues conspiracy theories, he has beliefs that are just not consistent with the state of Massachusetts," Doughty said of Diehl. "It makes him not electable."

Diehl sidestepped the assertion when asked about it, focusing on the primary and the spring GOP convention.

"So far he's got an 0-and-1 record," Diehl said. "At the convention, I think I beat him 71%-29%. So that claim, of course, is going to come from any challenger."

The most competitive high-profile Democratic primary Tuesday was for the nomination to succeed Healey as state attorney general. Former Boston City Council President Andrea Campbell, the first Black woman to serve in that job, will win the nomination, CNN projects. If she were to become AG, she'd be the first Black woman to be elected statewide. She will defeat labor attorney Shannon Liss-Riordan.

Healey, who has endorsed Campbell, stumped for her in the run-up to primary day. US Rep. Ayanna Pressley also backed Campbell and made her case at a rally with signs for all three women behind them.

"We need a bold, fierce, visionary, inclusive leader like Andrea Campbell," Pressley said. "The people deserve that. The moment demands that. And that is what the job requires."

Voters were thrown a late curveball when a third candidate, attorney Quentin Palfrey, dropped out last week and endorsed Campbell, joining Healey, Pressley and US Sen. Ed Markey in a race that has divided leading state progressives. (Palfrey was an active candidate when early voting began, and his name remained on the ballot.)

Liss-Riordan had the backing of Sen. Elizabeth Warren, Boston Mayor Michelle Wu and former acting Boston Mayor Kim Janey -- all three of whom featured prominently in her closing ad.

"Shannon Liss-Riordan is the progressive champion Massachusetts needs as our next attorney general," Warren said in announcing her endorsement late last month. "I know, firsthand, how Shannon fights back and wins against the corporations and special interests that take advantage of working families."

Campbell will face Republican attorney James McMahon, the losing 2018 nominee to Healey who ran unopposed Tuesday.

This story and headline have been updated with additional developments.