President Bartlet faces the biggest showdown of his re-election campaign on tonight’s “West Wing” (8 p.m., NBC). The brainy chief executive faces off in a single debate with his glib Republican opponent Robert Ritchie (James Brolin).

The debate might also provide some dramatic spark to an acclaimed drama that has clearly lost its way. “The West Wing” has always been preachy and self-important, and its characters have always been too smart and too articulate for their own good. But this year “The West Wing” has become tedious, unfocused and meandering, and its characters have become unlikable and underdeveloped. Does Toby’s anger and condescending nature stem from his infertility? Do we care? And romance-wise, Josh and Amy (Mary-Louise Parker) should either fish or cut bait. Their agonizing puppy-dog mutual infatuation has become insufferable. What ever happened to Sam (Rob Lowe)? In the series’s 1999 pilot, he was a brash fellow whose affair with a dreamy pot-smoking prostitute-law student (Lisa Edelstein) almost cost him his job. In the most recent “West Wing” episode, he was seen leading an Ivy League choir in a Latin sing-along. Bring back the old Sam.

Like most “West Wing” fans, I am critical of the show only because I expect so much from it. “West Wing” characters and viewers deserve better writing.

The forensics history series “Secrets of the Dead: Mystery of the Black Death” (7 p.m., PBS) examines the plague that annihilated up to 70 percent of Europe’s population between the 14th and 17th centuries. Modern-day medical sleuths scour birth and burial records in a single English town to determine just how many people avoided the disease, and whether these survivors shared genetic attributes that may have protected them from infection. Some scientists theorize that these lucky survivors married and passed along this immunity to their many ancestors. They believe that their genes may explain how some remain immune to current diseases, including AIDS.

Tonight’s other highlights

Scheduled on “60 Minutes II” (7 p.m., CBS): The eBay phenomenon; stock market manipulators explain their tactics.

Tennis star Serena Williams guest stars as Kady’s teacher on “My Wife and Kids” (7 p.m., ABC).

“Biography” (7 p.m., A&E) profiles actor John Ritter.

Van and Deaq take on a movie-obsessed Russian mobster on “Fastlane” (8 p.m., Fox).

A young musician discovers an enchanted guitar on “The Twilight Zone” (8 p.m., UPN). UPN has picked up this series for a full season.

“American Masters” (8 p.m., PBS) profiles a silent-movie great on “Lon Chaney: A Thousand Faces.”

A patient decides to stop his own heart on “Presidio Med” (9 p.m., CBS).

A tourist’s video may hold clues to a robbery/homicide on “Law & Order” (9 p.m., NBC).

A story about the hospital’s past disturbs Maggie on “MDs” (9 p.m., ABC).

Series notes

Two bickering disc jockeys ask Ed to officiate their breakup on “Ed” (7 p.m., NBC) … Carpooling woes on “The Bernie Mac Show” (7 p.m., Fox) … The ship rescues a colony exploited by Klingons on “Enterprise” (7 p.m., UPN) … Dawson thinks he’s seen a ghost on “Dawson’ Creek” (7 p.m., WB).

Variety follies on “Cedric the Entertainer Presents” (7:30 p.m., Fox) … Little League woes on “George Lopez” (7:30 p.m., ABC).

Globe trotting on “Amazing Race 3” (8 p.m., CBS) … Girls grovel for a guy on “The Bachelor” (8 p.m., ABC) … Helena discovers a foundling child on “Birds of Prey” (8 p.m., WB).