The former US vice-president John Nance Garner once described the vice-presidency as “not worth a bucket of warm piss”.

It was a memorable line, capturing something of the futility of playing second fiddle to the Leader of the Western World, but it also isn’t quite true.

Take the two vice-presidential candidates in this election, Senator Tim Kaine of Virginia and Governor Mike Pence of Indiana; the former describes himself as “boring” and the latter a “B-list” celebrity. Both realise this election isn’t about them, so dominant are their respective running mates, but they’re also plugging gaps in Secretary Clinton and Mr Trump’s appeal; Kaine when it comes to Latino voters and Pence with evangelical Christians.

Neither group has wholly warmed to the two presidential candidates, which is where the Spanish-speaking Senator and devoutly Christian governor come in. Beyond that, they’re clearly content to function as surrogates.

Thus Tuesday night’s televised debate lacked the theatre of the first presidential head-to-head. Neither candidate screwed up, but most pundits judged Pence the winner, his calm demeanour winning more stylistic points than Kaine’s slightly over-caffeinated approach.

Many of those tuning in would have been experiencing both candidates for the first time, for polls suggest around a third of voters know little about them, something confirmed by my failed attempts to engage people in conversation about their respective merits.

Besides, analysis of past vice-presidential debates show they have minimal impact on voting intentions. This one didn’t even manage to produce a memorable one-liner reminiscent of Democrat Lloyd Bentsen’s 1988 slap down of Republican Dan Quayle: “You’re no Jack Kennedy.”

Everyone remembers the line but few the candidate, and anyway the un-Kennedy-like Quayle went on to become vice-president. And although he subsequently faded into obscurity, it’s worth remembering that vice-presidents in the 1950s, 60s, 70s and 80s all went on to become president.

It’s that old line about being a heart-beat away from the White House. A bullet transported Lyndon Johnson there in 1963, and Watergate Gerald Ford a decade after that. Earlier this week I visited the Ford Presidential Museum in Grand Rapids, Michigan (just a few days after Trump), which commemorates his dramatic ascent.

Ford, uniquely, wasn’t elected to either office, but being a heart-beat (or scandal) away is more important given that Trump is 70 and Clinton will turn 69 later this month. And even in the likely event neither dies in office, being a vice-presidential candidate serves other purposes.

Pence’s stock among Republicans, for example, has undoubtedly risen as a result of Tuesday’s debate. So if the GOP crashes and burns come 8 November, Pence could emerge as its next nominee while Kaine becomes vice-president. That makes it worth rather more than a bucket of warm piss.