MONTGOMERY COUNTY’S all-Democratic delegation of state lawmakers in Annapolis includes a number of the General Assembly’s most senior and respected stalwarts. Despite that, its status as the state’s only county (or city) with a population exceeding 1 million, it doesn’t always exercise clout commensurate with its weight. Some promising newcomers might help. The following candidates, identified in bold type, are our choices in the contested Democratic primary races on June 24. (There are no contested Republican primary races in Montgomery.)

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District 14: There is no real race in this district that includes Damascus, Olney and Burtonsville. Three incumbents in the House of Delegates — Anne R. Kaiser, an energetic veteran, and a pair of first-termers, Eric G. Luedtke and Craig J. Zucker — face only nominal opposition from a challenger who has not mounted a viable campaign.

District 15: Two House incumbents in this big district, which stretches from North Bethesda and Potomac to Poolesville and Barnesville, deserve support for reelection. Kathleen M. Dumais has been a smart and effective member of the Judiciary Committee; Aruna Miller gained a spot on the powerful Ways and Means Committee in her first term and sponsored legislation to ban the sale of e-cigarettes to minors. The third delegate seat is occupied by David Fraser-Hidalgo, who was appointed to a vacancy last fall. One of only four Latinos in the legislature, he has been a quick study on the Environmental Matters Committee and should be returned for a full term. Challenger Bennett Rushkoff, a lawyer in the D.C. attorney general’s office, differs from his opponents only in offering unrealistic proposals, such as for a state-run health insurance program.

District 16: The best candidate to replace Sen. Brian E. Frosh, who is running for state attorney general, is Susan C. Lee, who has represented this district (including parts of Chevy Chase, Bethesda and Potomac) in the House for 12 years and has Mr. Frosh’s endorsement. Ms. Lee has been a leader in responding to the dangers of cybercrime and identity theft and has worked to protect victims of domestic violence and human trafficking. Her most serious challenger, Hugh Hill , is an emergency physician with an admirable record of medical service but less involvement in civic and political affairs.

In the House races, two incumbents — C. William Frick, an emerging leader, and Ariana B. Kelly — have worked hard for transportation funding, marriage equality and other priorities and both merit renomination. Among six challengers competing for the third seat, two stand out: Hrant Jamgochian, a health policy expert whom we endorsed four years ago, and Marc Korman, a first-time candidate who wins our endorsement this year. Either would be a highly able legislator, but Korman — an attorney, former aide to two Democratic members of Congress and local party activist — has the edge as someone who would focus on Montgomery’s transportation and school construction needs and who has the legislative smarts to be effective from Day One.

District 17: The retirement of Sen. Jennie M. Forehand has prompted one of the county’s most competitive races. The district includes Rockville and Gaithersburg. Luiz R.S. Simmons, who has served three terms in the House, is matched against Cheryl Kagan, who was a delegate from 1995 to 2003. Mr. Simmons is an intelligent and independent-minded legislator, but his mixed record on domestic abuse legislation in the Judiciary Committee gives the edge to Ms. Kagan, who is committed to strengthening protections for abused women.

Mr. Simmons’s departure leaves two incumbents, Majority Leader Kumar P. Barve and James W. Gilchrist, running for reelection in the House. Mr. Barve, a player in Annapolis, deserves another term, but Mr. Gilchrist, the son of a former Montgomery County executive, has accomplished little in his two terms. Two of the four challengers look like better bets: Susan Hoffmann, a former mayor of Rockville with extensive experience in promoting development, and Andrew Platt, an energetic former Capitol Hill staffer who has a good grasp of issues.

District 18: In what is likely a first for Maryland, an openly transgender candidate, Dana Beyer, is challenging an openly gay incumbent, Richard S. Madaleno Jr. , in the Senate race in this district stretching from Chevy Chase and Kensington to Wheaton. Both are knowledgeable and qualified, but this is not a close call: Mr. Madaleno is one of the ablest members of the Montgomery delegation and, with Mr. Frosh’s departure, stands to become one of its leaders. He is an expert in tax and budget matters and a pioneer in bringing marriage equality to Maryland, and he has been a force in keeping college affordable. Ms. Beyer is challenging him from the left, but there is little daylight between their positions.

Hints by three-term delegate Ana Sol Gutierrez that she might retire prompted a competitive campaign, even after Ms. Gutierrez chose to run again. Of the four challengers to the three House incumbents, Rick Kessler, a lobbyist for Chevron and other energy companies, has raised the most money, but Emily Shetty, a federal lobbyist for the Leukemia and Lymphoma Society, has a stronger grasp of the issues. She would be a better bet than incumbent Alfred C. Carr Jr., who has little to show for two terms in Annapolis other than unproductive tilting against the Purple Line transit project. Ms. Gutierrez, the most senior Latino representative in the legislature, is an effective representative of that community and deserves reelection, as does Jeffrey D. Waldstreicher, a reformist voice on the hidebound Judiciary Committee.

District 19: Sam Arora’s decision not to seek a second term in the House gives this district around Silver Spring an opportunity to elect Paul Bardack, a policy-oriented former federal housing official with extensive experience creating jobs in the private sector. He would round out a strong team anchored by Benjamin F. Kramer and Bonnie L. Cullison. Mr. Bardack’s idea of cutting corporate taxes to offset the impact of the state’s minimum-wage increase on small and mid-size businesses is a business-friendly proposal in a state that needs more of those.

District 20: Nine candidates want to represent this area that includes parts of Silver Spring and Takoma Park; just one, longtime House Ways and Means Committee chairwoman Sheila E. Hixson, is an incumbent. There is little ideological variation among the contenders, so voters will have to distinguish based on experience and personal qualities, which are generally strong in this bright, diverse field. We pick Ms. Hixson for another term employing her veteran’s clout on behalf of the county; Howard University business school instructor Darian Unger, for his technical smarts and life-saving experience as a volunteer firefighter; and Will Jawando for his energy and his work in the Obama administration building private-sector support for education reform.