Suck on it Pence. It’s a not a “tradition”, it’s just how things work out with ex-Presidents usually too old to campaign or can’t stand the new guy, like the Bushes.
It doesn’t happen often, but that’s just because it requires all these conditions:
- It must be a second-term president - if it’s a first-term president, he’s either running for re-election, or is not popular enough to be helpful.
- The second-term president must be popular enough to be helpful (that mostly ruled out G.W.Bush, who ended his second term at about 25% approval)
- The president must be healthy and capable enough to campaign (that ruled out Reagan, whose cognitive abilities were well on the downslide).
- The president must want to do it - and prior to 1990, the ideological and policy divide between the two parties was not remotely like it is today, and an outgoing president wouldn’t feel - as Obama surely, and correctly, does - that all his accomplishments would be reversed if his party lost the next election.