Credit: Via Joel Rubin/Twitter

The already large field of contenders for the District 8 Democratic congressional nomination expanded Monday, as former State Department official Joel Rubin of Chevy Chase announced he would join six other Democrats already vying to succeed Rep. Chris Van Hollen.

Until recently, Rubin, 44, was deputy assistant secretary of state for House affairs, which made him the department’s chief liaison to the U.S. House of Representatives during a period in which the Obama administration’s controversial Iran nuclear deal was being debated. Earlier, he was founding political and government affairs director for J Street, an organization established nearly a decade ago as a counterpoint to the more hawkish American Israel Public Affairs Committee in debate over U.S. policy toward Israel.

While vowing to “fight every day to effectively represent the progressive values that we hold dearly” in the district, Rubin added, “I think I can demonstrate a track record of success standing up for those values in the work I’ve done in the last two decades.” But, during a conference call with reporters, he sidestepped questions about how he differs from the other Democrats already in the race, other than to point to his experience as a congressional staffer and executive branch liaison officer.

“I understand how the building there works,” he said, alluding to the U.S. Capitol.

Rubin joins a Democratic primary field that already includes state Sen. Jamie Raskin of Takoma Park; Dels. Kumar Barve of Rockville and Ana Sol Gutierrez of Chevy Chase; former Obama administration official Will Jawando of Silver Spring; former Marriott International executive Kathleen Matthews of Chevy Chase; and David Anderson of Potomac, an official of a Washington-based seminar and internship program.

Except for Anderson, who entered the contest in mid-August, the other Democratic candidates in the primary field have been in the race since last spring—following Van Hollen’s announcement in March that he would vacate the seat to seek to succeed retiring U.S. Sen. Barbara Mikulski. The primary will be held April 26.

“This is a wide-open seat, as you saw in evidence from the debate the other night,” asserted Rubin, referring to last Wednesday’s environmental group forum in Silver Spring in which the six Democrats already in the race for the District 8 nomination participated.

Rubin, a Town of Chevy Chase resident for the past decade, said he will formally file as a candidate with the Federal Election Commission later Monday. He is entering a Democratic contest in which cost estimates for a winning campaign have started at $1 million and gone as high as $3 million to $4 million.

“The estimates are fair. It’s an expensive media market,” Rubin said. Without disclosing how much he hopes to raise and spend, he added, “We’re confident we can do what we need to do.”

Besides the Democratic contenders, Elizabeth Matory of Silver Spring—who unsuccessfully sought a Democratic nomination for state delegate in 2014—has filed to run in the general election as an independent. Meanwhile, it appears that as many as three Republicans are considering running in District 8, although none have filed official statements of candidacy with the Maryland State Board of Elections or the FEC.

Democrats in the district—which is centered in Montgomery County, but also includes parts of Carroll and Frederick counties—enjoy a nearly 2-1 advantage in voter registration.

The three Republicans—Gus Alzona of Bethesda, James Calderwood of Chevy Chase and Bill Day of Bethesda—appeared at a brunch sponsored by the Montgomery County Young Republicans late last month. Their talks were videotaped by A Miner Detail, a local politics blog.

Calderwood, a Washington-based attorney who was recently named by Gov. Larry Hogan to chair the Maryland Transportation Commission, told Bethesda Beat in August that he was considering entering the race. He said in a phone interview late Sunday that he hopes to make a decision this month.

“I’m still gathering information and talking to a lot of people,” said Calderwood, adding, “I’m looking at it strongly.”

In his recent appearance before the Young Republicans, Calderwood said, “I have been spending the last six months meeting with all kinds of people who can write checks of $2,700”—a reference to the maximum amount that an individual is currently allowed to donate to a congressional candidate per election.

“If we have a candidate who’s not prepared to raise $1.5 million, forget it, that person is not going to win,” declared Calderwood, while reiterating past statements that he would put “a fair amount of my own money” into the contest if he runs.

Day, a Naval Academy graduate who has a law practice in Rockville, started a website for the “Bill Day Exploratory Committee” last month.

“We can take District 8—it’s not impossible,” Day told the Young Republican gathering, raising the prospect of “some of the moderate Democrats” joining with Republican and independent voters. The district has more than 100,000 “unaffiliated” voters—independents who have not registered with a political party.

Alzona, a certified public accountant, has run for Congress twice before in District 8. In 2012, he finished last in a four-person field seeking the GOP nomination; in 2006, he ran third among three candidates in the Republican primary.

Currently an at-large member of the Montgomery County Republican Central Committee, Alzona noted at last month’s brunch that he is the “only Maryland Republican official” to have endorsed the presidential candidacy of conservative Texas Sen. Ted Cruz.