It’s an event everyone usually ignores. Except for tonight.

Once every four years the candidates running for vice -president of the United States square off against each other in a televised debate. Other than political junkies, no-one watches.

Being vice-president is a thankless task in America. You have no real job description; you just have to be prepared to become president without warning. Not that it happens very often.

Except this year, with a 73-year-old running against a 78-year-old (by inauguration day) you have to wonder what are the chances of either candidate living through the full four-year term. Old white men are known to die when stressed, and it is tough to imagine a more stressful job.

Which means tonight is an audition of sorts for Mike Pence and Kamala Harris. I can’t say that they are both non-entities, but I had to check to make sure my memory was correct and that Pence really was vice-president. Harris I knew – but she was in the news just last month.

Given that one of them may be president before voters go to the polls in 2024, it would make sense to check out what they have to say on the issues. Their views may not mean much today – but they might in two years’ time.

Mind you, it has been a long time since an American president died in office of natural causes (Franklin D. Roosevelt in 1945). It has been almost 60 years since John F. Kennedy’s assassination propelled Lyndon Johnson into the presidency. And more than 40 years since Richard Nixon’s resignation gave the presidency to Gerald Ford.

And, while many think the vice-presidency is a stepping stone to the top job when the incumbent retires (most recently George H.W. Bush more than 30 years ago), that hasn’t been much in evidence in recent years. There was no President Mondale, or President Gore (okay, that one may have been stolen), no Quayle or Cheney. Joe Biden may break the trend, but I wouldn’t bet on it.

Tonight though is different. These days the average life expectancy of an American male is 78 years. That means Donald Trump is approaching his “best before” date, and Joe Biden is there already.

But that isn’t the whole story, just the current average. White males born in 1946, like Trump, have a life expectancy of 72 years. for those born in 1942, like Biden, it is 71 years.

Do you see why tonight’s debate is important? Both major parties are offering candidates who have already passed their life expectancy. There is a strong possibility one of the two debaters tonight will become president before the next election.

As an historical note, sometimes timing is everything. Every American knows Franklin D. Roosevelt died in office and was succeeded by Harry Truman. But many probably don’t realize Truman was new to the job. He was Roosevelt’s third vice-president.

John Nance Garner was VP for Roosevelt’s first two terms, then Henry A. Wallace until 1945. If Roosevelt had died earlier one of them would have inherited the top job. (After Roosevelt term limits were imposed on presidents.) But Wallace was replaced by Truman for the 1944 campaign, as he had replaced Garner four years earlier.

So tonight’s debate is important to watch. I have no idea what the candidates will say – but I think I can guarantee it will be a more civil discussion than last week’s clash of presidential candidates.

That is probably a good thing.