John Delaney (D-Md.). (Nick Wass/Associated Press)

MARYLAND REP. John Delaney (D) is among a tiny handful of lawmakers who have managed to surmount partisan gridlock to make a quick, positive mark in Congress. In just two terms representing the state’s 6th District, which stretches from Montgomery County to the West Virginia line, Mr. Delaney has established a reputation as one of Capitol Hill’s most substantive, proactive and bipartisan newcomers.

In plenty of places, Mr. Delaney, who had a successful business career before turning to politics in 2012, would be a shoo-in for reelection. But Maryland’s 6th, closely divided between Democrats and Republicans, is nobody’s safe seat. Having won a second term narrowly in 2014, Mr. Delaney faces a tough fight again this year.

We have endorsed him on the strength of his energetic advocacy of bipartisan legislation, including a measure that would encourage corporations to repatriate overseas earnings tax-free, in exchange for helping finance major infrastructure projects.

That bill, which has dozens of Republican sponsors, is one of several he conceived that attracted bipartisan backing. The nonpartisan site GovTrack ranked Mr. Delaney third highest for bipartisanship among all House Democrats; last year, nearly two-thirds of his bills and resolutions had both Democratic and Republican co-sponsors.

His Republican challenger, Amie Hoeber, a defense consultant, is the beneficiary of ample campaign cash, much of it from her husband. She has sought to play on voters’ anxieties by insisting they live in “an era of fear that didn’t exist a decade ago.” (Never mind the aftermath of Sept. 11 or the London bus bombings of 2005.)

Ms. Hoeber’s stock in trade is a trove of alarmist assertions. But her policy prescriptions are facile. She proposes to increase military spending by tens of billions of dollars, airily suggesting the funds could be gotten by cutting “duplicative programs” she does not name. Just as implausibly, she says Metro, facing huge deficits and infrastructure projects, can solve its problems without more revenue.

Meanwhile, like many in the GOP, Ms. Hoeber has found herself in a morass of hypocrisy regarding Donald Trump, whom, as a loyal Republican, she backs as a “matter of honor.”

Where is the honor for Ms. Hoeber, who boasts of mentoring young women and fighting gender discrimination and domestic abuse, in supporting a leering misogynist who has publicly objectified women for decades and stands accused of groping and assaulting them?

Ms. Hoeber is a standard-issue partisan with no fresh ideas; Mr. Delaney is an original thinker and a leader. The district would be well served by reelecting him.