U.S. Sen. Barbara Mikulski has long been a phenomenally popular political figure in this state. She may be short in stature, but she is fearless, feisty and as authentic as a box of Old Bay seasoning. Just ask the voters of Maryland. To them, she's still the same neighborhood activist from Highlandtown who fought an ill-considered waterfront highway and was elected to the City Council in 1971 and the U.S. House of Representatives five years later.

So in deciding who should replace “Senator Barb” now that the 79-year-old has decided to end her reign as the longest-serving woman in Congress, voters ought to ask themselves: Who would best carry on the traditions of the indefatigable Ms. Mikulski, a woman whose crusades for social welfare issues such as equal pay and child care won her a national following but who also found the time to stand up for the broader interests of Marylanders — from securing guest worker visas for immigrant crab pickers to retaining thousands of federal jobs from the Centers for Medicare & Medicaid Services to the Hubble Space Telescope and Goddard Space Flight Center?

In the hard-fought Democratic primary, the choice is clear: Rep. Chris Van Hollen Jr. is by far the most qualified candidate to carry on the Mikulski tradition. The seven-term congressman from Montgomery County has demonstrated the same kind of leadership skills and devotion to progressive causes whether in the halls of the state Senate in Annapolis or in Congress. His rise from Rep. Connie Morella's successor in 2003 to then-Speaker Nancy Pelosi's assistant three years later marked his arrival as someone who could get things done within the chamber.

Mr. Van Hollen's record has not simply been about casting votes when called to the floor but about shepherding legislation, whether it involved reducing the interest rates on student loans or providing health insurance to millions of Americans who couldn't previously afford it. Even as Capitol Hill grew increasingly partisan, Mr. Van Hollen demonstrated a willingness to reach across the aisle — helping negotiate bipartisan budget agreements from his post as a senior member of the House Appropriations Committee, for instance. His extensive knowledge of the federal budget often made him the go-to man when his party needed someone to counter the misguided fiscal assertions of Rep. Paul Ryan and others in the GOP.

Rep. Donna F. Edwards of Prince George's County, his main opponent in the primary field, represents a remarkable success story herself. A single mother and community activist noted for her work against domestic violence, Ms. Edwards became the first African-American woman to represent Maryland in the U.S. House of Representatives when she was first elected in 2008. She would be only the second African-American woman to serve in the Senate (Carol Moseley Braun having been the first nearly a quarter-century ago) and the first African-American, man or woman, to win statewide office in Maryland on his or her own.

Bringing greater diversity to the Senate is a commendable goal (there are currently only 20 women and two African-Americans, both men, in the chamber), and the body could use Ms. Edwards' perspective, not just as a minority but as a single parent who has struggled economically in her life. She is a persuasive spokeswoman for progressive values, and against most any other opponent, we would be happy to endorse her, but Mr. Van Hollen's record of accomplishment is simply without peer.

We have also been troubled by the dishonesty of some of Ms. Edwards' campaign ads — most recently an assertion that Mr. Van Hollen is somehow soft on gun control and thus on crime. The evidence? His sponsorship of a 2010 campaign finance bill known as the DISCLOSE Act that expanded disclosure requirements for large donors but not for the National Rifle Association (or trade unions for that matter). It was a bill supported by this newspaper despite its exemptions and by 217 of 253 Democrats voting in the House only to fail in the U.S. Senate because it lacked a filibuster-proof majority due to GOP opposition.

The claim that Mr. Van Hollen has somehow failed his constituents by not taking positions that are liberal enough is a theme that has pervaded Ms. Edwards' campaign. In reality, the two candidates have nearly identical voting records, and if this newspaper is going to rail against Republican intransigence in Congress — as it has loudly and often — we can scarcely approve of a candidate from the other side of the aisle who touts an unwillingness to compromise as a virtue.

As a senator, Ms. Edwards would likely draw much attention from the media and would no doubt use that platform to express her strongly progressive views. But that's not the same as actually writing or sponsoring meaningful legislation and convincing a divided Congress to support it. Mr. Van Hollen offers the best chance of achieving that goal — and of standing up for worthwhile federal spending in Maryland as he's so often done in the appropriations committee and as Senator Mikulski has so often done in the upper chamber.

In the year of the political outsider, the Edwards-Van Hollen matchup represents two insiders with diametrically opposite approaches to the job. Giving heartfelt speeches on the steps of the Capitol may be stirring for the Democratic base, but it's scarcely the same as serving in leadership and having the kind of impact Mr. Van Hollen has had in the House. Ms. Edwards has done an admirable job representing the voters of Maryland's 4th Congressional District and has a compelling perspective, but it is the highly effective Mr. Van Hollen who should succeed Barbara Mikulski in the U.S. Senate.