Voters intuitively know that, because Trump is the oldest presidential nominee ever, there is a higher than ever probability that, if Trump is elected, his vice president would have to assume office.
The Social Security Administration publishes
actuarial estimates of dying within one year. The probability that someone Trump's age will die within one year is 5.3%. That probability increases each succeeding year, until it reaches 8% during Trump's last year in office. When you cumulate the probabilities, you'll see that President Vance is both a possibility and a probability. Those statistics are just about death. They don't even take disability into consideration.
That's why conservative media outlets are pushing this story.
At the link above, you can look up the probability that you will survive another year. Always fun.