Democratic primary candidate Kathleen Matthews, during a debate for the Maryland 8th Congressional District seat. (Evelyn Hockstein For The Washington Post)

Potomac wine merchant David Trone entered Maryland’s 8th Congressional District Democratic primary last week as a first-time candidate promising an alternative to Washington politics-as-usual.

On Tuesday, he announced that he had fired three staffers from his fledgling campaign for one of the oldest types of ­election-season deception — posing as volunteers for his two principal opponents, state Sen. Jamie B. Raskin and former Marriott executive Kathleen Matthews.

Trone did not name the staffers or offer details of their activity.

“Today, I learned that young people working for my campaign surreptitiously volunteered for the campaigns of other candidates in the race,” he said in a statement. “After investigating the incident, I terminated those two employees and their supervisor effectively [sic] immediately.

“I called Kathleen Matthews and Jamie Raskin to apologize and to assure them that this activity is unacceptable and contrary to how my campaign will operate. Everyone in my campaign understands that they are expected to meet the highest standard of behavior when acting on my behalf.”

David Trone (Trone family photo)

Calls to Kurt Staiger, Trone’s campaign manager, were not returned. Communications director Mary Werden said she had no details on how long the workers were involved with the other campaigns or what they did. She also declined to name them.

“These people are young. They made a mistake,” Werden said. “We certainly don’t want this to follow them through their career. We’ve investigated, they were removed from the campaign, and we’re moving forward.”

The Matthews campaign identified one of the Trone staffers as Joseph Butensky, whose LinkedIn page describes him as a 2015 American University political science graduate and former intern for U.S. Rep. Kathleen Rice (D-N.Y.). Butensky did not return phone calls.

In a letter to Staiger on Tuesday morning, Matthews’s campaign manager, Ethan Susseles, said that on Monday, Butensky returned from what should have been a two-to-three-hour neighborhood canvass in 45 minutes. Calls to the addresses on Butensky’s route determined that the doors had not been knocked on.

Susseles said Butensky “proceeded to walk around our office and attempted to enter the senior staff office.” After another staffer blocked him, Butensky left.

The volunteer coordinator for Matthews recognized Butensky as someone he attended college with, Susseles said. An online check turned up his LinkedIn page, which identified him as “Field Organizer at David Trone for Congress.”

Susseles said any question about Butensky’s affiliation was eliminated when the letter from the Matthews campaign was hand-delivered to Staiger. An email back from the courier showed that Butensky signed for it, Susseles said.

The Matthews campaign had intended to keep Butensky’s name out of the letter and redacted it in six spots but missed one.

Susseles told Staiger that the campaign was “very disappointed,” not only for ethical reasons but also because the incident — which was first reported by Bethesda Beat — happened less than 24 hours after Trone called Matthews to pledge “a clean, positive campaign.”

“We understand your candidate has virtually unlimited resources,” Susseles wrote in the letter, referring to the wealthy Trone’s pledge to spend “whatever it takes” of his own resources to win. “We hope that you will restrain from using them to plant people in our campaign office. Please cease and desist immediately.”

Raskin said that while his campaign had suspicions about several volunteers, he had no concrete evidence until he saw ­Trone’s statement. Raskin said he is drafting a letter to Trone and wants to know the identity of the person or persons who infiltrated so he can determine whether any strategic information was stolen.

“It doesn’t exactly sound like Watergate,” Raskin said. “It sounds like an act of amateur espionage and infiltration.”