THE CONTRAST was stark between Reps. Donna Edwards and Chris Van Hollen, chief rivals in Maryland’s April 26 Democratic primary, despite them being a pair of liberals with similar voting records. In their first debate, Ms. Edwards began and concluded her pitch to voters with an assertion of identity — namely, hers as an African American single mother, a “unique voice” who could channel the interests of the disadvantaged and dispossessed. Mr. Van Hollen started and ended with an argument — one echoed by dozens of elected officials who support him — that his record of accomplishment has and will deliver not only votes and speeches, but also results.

For voters frustrated with gridlock and hyper-partisanship in Washington, the Edwards-Van Hollen debate offered a moment of clarity. Mr. Van Hollen, who represents the 8th Congressional District, has an undeniable record as a deal-maker with a knack for creative compromise in a Congress where that skill is a rare commodity; Ms. Edwards, the incumbent in the 4th Congressional District, attacked him for it, declaring she would never bend “when it comes to our principles.”

Friday’s debate, on WAMU-88.5’s Kojo Nnamdi Show, at times wallowed in competing claims of support from various Democratic interest groups. Yet beneath the tedium was a core truth: that while Ms. Edwards is right that women and black people are underrepresented in the U.S. Senate, most elected female and black officials in Maryland who have made endorsements are backing Mr. Van Hollen, who is white.

There’s a reason for that. While no one doubts her political savvy or policy chops on issues she cares about, Ms. Edwards is widely seen as less interested in crafting legislation and tending to the weeds of local funding and projects than in staking out ideologically pristine positions, even if they contribute to partisan paralysis.

In the debate, as she has on the stump, Ms. Edwards dismissed Mr. Van Hollen as a standard- bearer of the establishment. In her own telling, she is, by contrast, someone who overcame a modest upbringing and has “walked in the shoes of the people I hope to represent.”

That would be a more compelling argument if Mr. Van Hollen were a run-of-the-mill backbencher with a legislative record as modest as Ms. Edwards’s own. In fact, he is among the most highly regarded Democrats in the House, renowned for his command of the federal budget and innovative legislative approaches to tackling climate change. Mr. Van Hollen has been a key negotiator in efforts to break logjams in the House, and he likely would play a similar role in the Senate on issues where bipartisan compromise may be possible, such as criminal justice reform. It’s impossible to imagine Ms. Edwards playing a comparable role — a point she herself confirmed by attacking those who would compromise “just to make a deal and get their names on something.”

Well, exactly: Ms. Edwards is unlikely to have her name on successful legislation. Her allergy to compromise, comparable to the disdain expressed by tea party Republicans, is what has brought Congress to a standstill. She is proof that doctrinaire ideology is alive and well on both sides of the aisle. Mr. Van Hollen, on the other hand, might chip away at it.