Baltimore County Executive Kevin Kamenetz — a veteran politician who was running for Maryland governor — died of cardiac arrest early Thursday, upending a crowded Democratic primary race just weeks before the election.

Kamenetz, 60, awoke not feeling well at 2 a.m., officials said, and traveled by car with his wife to a volunteer fire station two miles from his home. They called 911 from the parking lot, and Kamenetz spoke to the operator. But he soon lost consciousness, and medics could not revive him.

Hours earlier, Kamenetz and three other Democrats vying for the nomination had participated in a candidate forum in Prince George’s County. He introduced himself by saying he was a “lifelong Marylander and a lifelong Democrat” and said he was “blessed with a loving wife of almost two decades, Jill, and . . . two teenage sons,” Karson and Dylan.

Kamenetz was one of seven major candidates running to challenge Gov. Larry Hogan (R). He, Prince George’s County Executive Rushern L. Baker III and state Sen. Richard S. Madaleno Jr. were the only candidates who have experience in elected office.

In the most recent independent polls, in February, Kamenetz scored near the top of the pack, behind Baker and former NAACP chief Ben Jealous. A large percentage of Democratic voters remained undecided, and analysts say they expect most voters to tune in to the race in the final weeks before the June 26 Democratic primary.

Kamenetz had more campaign cash than any other Democrat at the start of this year and was counting on a strong showing in Baltimore County — a key ­general-election battleground — to propel him in the primary. His campaign recently purchased television ads to run in the Baltimore and Washington markets in the final two weeks of the race.

“It really does make a race that was already unsettled even more unsettled,” said Todd Eberly, a political-science professor at St. Mary’s College. “He was drawing somewhere near 20 percent of the vote, and now those folks need to reassess who they want to support . . . look to other folks in this race and see if there is someone who appeals to them the way Kamenetz did.”

Hogan ordered Maryland flags lowered to half-staff from Thursday through sunset on the day of Kamenetz’s funeral, which is scheduled for Friday. “We join with the citizens of Baltimore County and all Marylanders in mourning,” the governor said in a statement.

Kamenetz grew up in Lochearn, Md., the youngest of five children. He worked at the drugstore his father owned and attended Johns Hopkins University and the University of Baltimore School of Law. He was a prosecutor in the Baltimore state’s attorney’s office before being elected to the first of his four terms on the Baltimore County Council.

He proudly told prospective voters that he had never raised property tax rates during his 7 1/ years as county executive.

Known as a blunt, at times hard-charging politician, Kamenetz clashed with Hogan on issues including school funding and the environment. On the campaign trail, he pledged to fight for Maryland workers, including a push for a statewide $15 minimum wage and an expansion of job-training programs.

He was lighthearted before he entered the forum Wednesday evening at Bowie State University, joking with reporters about having seen them at a different forum the night before. He told the sparse crowd that Baltimore County built 90 schools during his tenure as executive, had rising graduation rates and that “there is no disparity in graduation rates between black and white students.”

“I have made education a priority,” Kamenetz said. “If we focus again on our educational system, that’s how we grow jobs.”

State election board officials were somewhat uncertain Thursday how Kamenetz’s death will affect state ballots. His running mate, former Montgomery County Council member Valerie Ervin, has until May 17 to decide whether she wants to designate a new gubernatorial candidate for the ticket, said Jared DeMarinis, director of candidacy and campaign finance for the State Board of Elections.

DeMarinis said Ervin can designate herself or someone else. If she decides to run for governor, she will select a new running mate.

Kamenetz’s name is on ballots that will soon be mailed to members of the military living overseas, DeMarinis said. He said it was unclear whether his name will remain on ballots when voters go to the polls next month. “Essentially, a vote for Kamenetz could equal a vote for Ervin and a new candidate,” he said.

Politicians across the state offered their condolences Thursday, with many of them saying they would suspend their campaign plans as a sign of respect. U.S. Sen. Benjamin L. Cardin (D-Md.) said in a tweet that Kamenetz was “a true public servant. He lived a life dedicated to helping others.”

Baltimore County officials said Kamenetz said he didn’t feel well when he awoke early Thursday at his home in Owings Mill, Md. From the parking lot of the Chestnut Ridge Volunteer Fire Company, he told a 911 operator he was experiencing tightness in his chest.

Volunteer medics roused by the call left the station and provided assistance, using a defibrillator and performing CPR, said Elise Armacost, public affairs director for the county fire and emergency medical services department. But his condition “quickly deteriorated.”

At one point, Armacost said, volunteers were able to restore his pulse and administered an IV to prepare him for advanced life-support measures. He was taken to University of Maryland St. Joseph Medical Center, where he was pronounced dead at 3:22 a.m.

“By all accounts he appeared to be in excellent health,” Armacost said. “He saw a doctor regularly, ate well, liked healthy foods. . . . He liked yogurt and granola.”

Kamenetz recently announced an initiative to remove junk foods from county vending machines. “This was not a person who had unhealthy habits,” Armacost said.

Kamenetz’s funeral is scheduled for Friday at 2 p.m. at Baltimore Hebrew Congregation. Hogan and other elected officials from across the state are expected to attend.

Dana Hedgpeth contributed to this report.

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