Vowing to fix “a broken system,” Republican John Deaton returned to the political arena on Monday night, launching a bid for U.S. Senate in 2026 that he says will disrupt the status quo, bring down costs and make one of the most expensive states in the union affordable again.

“I got in this race because Massachusetts is in trouble,” Deaton, 58, of Swansea, told a crowd of several hundred supporters at Off the Rails, a Worcester restaurant.

Deaton’s target: Veteran U.S. Sen. Ed Markey, D-Mass., who’s spent a half-century on Capitol Hill, and remains the polling favorite to capture the Democratic nomination next year.

Pointing to the rising cost of everything from groceries and natural gas to rent and electricity, Deaton argued that Markey, who first entered public life when he was in elementary school, had lost touch with the pressures facing working families.

“I’m sorry, Ed. After 50 years of living in the swamp, you can’t relate,” Deaton said.

In a campaign video released ahead of his announcement, which was also played at the Worcester launch party, Deaton called Markey “MIA.”

But he’ll still have to prove he’s a viable alternative.

Deaton, a crypto attorney and Marine veteran, unsuccessfully challenged U.S. Sen. Elizabeth Warren, D-Mass., in 2024. He lost to Warren, of Cambridge, by a margin of 60%-40% on Election Day.

Speaking to reporters after the event, Deaton said he hoped woo disaffected Democrats and the large swath of unenrolled voters who make a big chunk of the state’s electorate.

Deaton had been teasing a bid for weeks ahead of the Monday night announcement as he let supporters know about his “special event” in the city roughly equidistant to both Springfield and Boston.

Guests braved an insistent rain and heavy traffic on the Massachusetts Turnpike to make it to the early evening event.

An hour before its scheduled start, the room filled with cocktail banter, and an acoustic duo provided a country-inflected soundtrack.

State Republican Party Chairperson Amy Carnevale castigated both Warren and Markey for what she described as their obstructionism during the federal government shutdown.

“Massachusetts residents deserve to have a federal government that is open, that is working,” Carnevale said. “A clean continuing resolution was presented, and we had our incumbent senators, both of them voted against it. We need to... have change.”

Deaton’s audience on Monday also included two of the three GOP hopefuls for governor in 2026 — Mike Kennealy and Brian Shortsleeve — as well as Bay State Republican royalty.

The third, medical device millionaire Michael Minogue, had a conflict and was unable to attend, Deaton said.

Kennealy, a former top official to former Gov. Charlie Baker, offered some opening remarks, telling the crowd that it was time to “send Ed Markey into retirement.”

Shortsleeve, also a former Baker administration official and a Marine veteran. told the crowd that “we can win this race. We will win this race. And we must win this race.”

State Sen. Peter Durant, R-Worcester/Hampshire, told MassLive that he’s looking forward to a lively race, and one where Deaton, tested by his first campaign against Warren, puts those lessons into practice.

“You learn from your mistakes and you amplify what works,” Durant, who’s toyed with bids for higher office in the past, said. “There are a lot of unknowns so far, but it’s a good start to the election season.”

In an interview with MassLive earlier this month, Deaton remained much the same candidate he was two years ago, when he tried to meld working-class populism with a socially moderate message.

He’s still not a fan of now-President Donald Trump (he thinks, for instance, the Republican has gone too far with his hardline immigration policies). He still supports abortion rights and marriage equality.

He said he’s looking forward to drawing bright-line distinctions on those and other issues, including climate change, against Markey.

As he did two years ago, Deaton spoke at length on Monday about his hardscrabble roots in a crime-ridden Detroit neighborhood — and laid out in his memoir “Food Stamp Warrior."

“People are struggling, and I know their struggles, because I have lived through them,” he told supporters. “My superpower is that I truly believe that tomorrow will bring a better day. It’s what got me where I am in life.”

“I went to bed hungry,” he continued. “My worst childhood memory is listening to my mother cry herself to sleep on the nights when we went to bed hungry and we didn’t know where the food was going to come from for the next couple of days.”

“I am running because I am one of you,” he said.

While Deaton may be aiming for Markey, it’s not a guarantee that he will be his eventual general election opponent.

Markey, 79, faces a primary challenge from U.S. Sen. Seth Moulton, D-6th District, the 47-year-old Marine veteran from Salem, who has made Markey’s age and the need for generational change on Capitol Hill one of the animating principles of his candidacy.

Alex Rikleen, a former school teacher from Acton and a political newcomer, is also seeking the Democratic nomination next year.

In a statement, Markey’s campaign manager Cam Charbonnier argued that Deaton had “already tested his message against the record and lost in a landslide.”

“If he wants another round, fine. This state doesn’t elect MAGA yes-men,” he continued. “We elect leaders who actually get results — like Ed Markey," he said.

Moulton told MassLive that he believed “Massachusetts voters deserve a choice.”

“And so, you know, I welcome anyone who wants to get into the race,” Moulton said after an annual town hall for veterans in Marblehad. “But I’m going to stay focused on what Massachusetts families need.”

MassLive Reporter Tréa Lavery contributed to this story.