But what they've almost never done is walk unannounced through a town centre, greeting unvetted members of the public. Neither of the two serious contenders for No 10 has had the nerve to copy John Major's gamble from the 1992 campaign, which saw him standing on a soapbox in the street with a loudhailer, attracting abuse but also respect.
Instead, for the party leaders this has been a campaign of sterile photo opportunities and freeze-dried speeches. Every moment has been rigidly stage-managed. No spontaneity, no unpredictability, no risk.
The one party leader who does frequently pound the streets is Nicola Sturgeon - but, given that her Scottish National Party is apparently on course to win every seat in Scotland, the chances of her encountering meaningful opposition are slim.
The campaign has felt like a sham.
I suspect that - like so much in politics these days - it's largely due to the Scottish referendum. That campaign, especially its final two weeks, was for Westminster politicians a horror show.
John Prescott was remorselessly heckled ("Bampot! Mental case!"). Jim Murphy, the Scottish Labour leader, was pelted with eggs. A hundred Labour MPs were pursued through Glasgow's centre for 15 minutes by a nationalist on a rickshaw blaring out the Darth Vader theme and shouting, "Bow down, people of Glasgow! Bow down to your imperial masters!"
This, party strategists must have concluded, is what we get for venturing out in public. Never again.
There has been the odd moment when a major leader has been caught off guard. In five weeks Ed Miliband has had one unscheduled encounter: on a visit to Chester he was engulfed by a delirious hen party. (As a rule, though, he never goes anywhere without a lectern to act as a barrier between him and the electorate.)
In Solihull, a young man mooned at Nick Clegg in the street. On a walk through Northumberland, a busker with a ukulele serenaded Cameron with a specially composed ballad entitled F*** Off Back to Eton. The next week I happened upon Cameron waiting on the crowded platform of Bedford station for a delayed train to London. He was concentrating grimly on not meeting commuters' eyes. Eventually a woman trotted up and asked him for a photo; Cameron smiled weakly, obliged, then went back to fretting about his train.
Ukip's Nigel Farage invited me and a couple of other journalists to follow him as he knocked on doors one evening in South Thanet. After a while, though, I noticed a curious pattern: every door Farage chose to knock on was opened by someone who was either a) definitely voting for Ukip, or b) considering whether to vote for Ukip. Was Farage almost universally popular? Or was he deliberately taking the press only to houses vetted in advance by his activists? When I put this to Farage, he seemed appalled by my cynicism.
An unintended consequence of party strategists' neurotic risk-aversion is that, on the rare occasions when leaders have slipped up, the blunder has received far more media attention than it otherwise would have. Take, for example, when Miliband unveiled his preposterous pledge rock, carved with feeble platitudes ("An NHS with time to care"). Perhaps he could also have the pledges tattooed on to his forehead, backwards, so he's reminded of them every time he looks in the mirror.
Even Labour supporters winced at the absurdity of this stunt; just as Tory supporters winced when Cameron earnestly told Asda staff that they must all remember to vote because this would be a "career-defining" election. He meant to say "country-defining".
What makes the timidity of this whole campaign so frustrating is that, even from the parties' point of view, it's probably counterproductive. It means that, at best, leaders will only maintain their existing support, rather than winning over people who normally vote for their opponents.
On Wednesday Cameron spoke at a utilities firm in north London. Unusually, a member of staff dared to ask the Prime Minister a hostile question. Cameron raised his voice to be heard above the audience's applause. "Thank you for your lively question!" he cried. "We don't want controlled events!"
He should have told his strategists that.