Fans of “The West Wing” will tune in tonight armed with more knowledge than we really want.

Its first new episode in weeks, the White House drama (8 p.m., NBC) will focus 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 outcome of this presidential campaign – a secret well-protected by the show’s producers – now faces their urgent reappraisal.

But for viewers, 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 one mean spoiler.

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 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 said during a June 2000 interview (by which time 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.