We fans of "The West Wing" will tune in Sunday night armed with more knowledge than we really want.

Its first new episode in weeks, the White House drama will be focusing on vice presidential candidate Leo McGarry as he preps for a high-stakes debate with his Republican rival. This is also the first new episode to air since the death of John Spencer, who had given life to Leo since the series began in 1999. ("The West Wing" airs 8 p.m. EST on NBC.)

The outcome of this presidential campaign — a secret well-protected by the show's producers — now faces their urgent reappraisal.

But for the audience Sunday, such narrative concerns will be upstaged by an actor whose personal narrative was cruelly cut short. Spencer's death from a heart attack on Dec. 16 — four days shy of his 59th birthday — was news no viewer could avoid or dismiss. That's one mean spoiler.

It is also a reminder of how powerfully we bond with our friends on TV.

From the first episode of "The West Wing," we loved Leo. Honest, tough but a softie, with a mischievous grin only sparingly deployed, he was (or shouldn't we say "is"?) world-weary yet tireless — whether as chief of staff to the incumbent president (Martin Sheen), or more recently as running mate alongside the Democratic presidential hopeful, played by Jimmy Smits.

There were obvious parallels between Spencer and McGarry: Driven and passionate in their chosen careers; both known as good men.

They both were also alcoholics, although this likeness was only by chance, Spencer told me during a June 2000 interview (by which point he had logged 11 years in recovery to McGarry's eight).

"Just the fact that I am here today is a miracle," he said, clearly grateful for kicking his habit. "It's extra innings."

Those extra innings included playing Leo on "The West Wing."

Spencer will appear on two more episodes after this Sunday, according to NBC. Because of pre-emptions for Winter Olympics and other specials, the last of the five episodes now wrapped won't air until March 19.

Then what? Maybe, as with Spencer, a heart attack will spell his character's doom. (In an eerie foreshadowing, Leo suffered a nearly fatal coronary on an episode that first aired in fall 2004.) Just how the campaign plotline, and the series overall, should be retooled to give Leo a graceful send-off is the sad creative challenge with which "West Wing" producers have now begun to grapple.

Meanwhile, we must get used to thinking of Spencer in the past tense, even as he plays before our eyes.

We went through this process little more than a year ago with Jerry Orbach.

Orbach had capped a long career in theater and films with his TV role as sardonic, seen-it-all Detective Lennie Briscoe, whom he played for 12 seasons on "Law & Order." We were looking forward to seeing him take Briscoe to a "Law & Order" spinoff. Then, shortly into production of "Law & Order: Trial By Jury," Orbach died at 69 of prostate cancer.

Last year, of course, also saw the death of Johnny Carson, the king of late night who had left his "Tonight" throne a decade earlier. And ABC News' Peter Jennings died a few months after making what would prove his final TV appearance: a brief announcement that he was battling lung cancer and would be off for a while.

Each in his own way, Carson and Jennings were great TV comrades. Both live on in our memories, if not on the air.

But actors enjoy special here-but-not-here status from their viewers.

We love them, yet connect with them not so much through who they are as through the characters they play on their comedies and dramas.

And when they die we deftly navigate the contradiction that, sure, they're gone, but thanks to their characters they'll never go away. They're dead but recur in an endless afterlife.

Orbach lives on as the dutiful Briscoe night after night in "Law & Order" reruns.

Or consider Lucille Ball, dead since 1989. A half-century after she emerged as Lucy Ricardo, she is still stomping grapes and chugging Vitameatavegamin, as she will in perpetuity.

Such immortality on TV is attainable, even commonplace, when it is earned. Among our TV friends, including Leo McGarry, some not only outlive the actors who portrayed them. They will survive us, too.