The 4 leading candidates to challenge Trump in 2020 are currently:
Biden leading with 33% (he will be 78 years old in Autumn 2020)
Bernie Sanders at 13% (79 years old)
Kamala Harris with 9%
Elizabeth Warren at 8%. (71 years old and already effectively counted out for naively taking the Pocahontas bait)
So let's hope Kamala Harris is the one, or someone else comes to the fore after the mid-terms. All I'm sure is if the focus continues to be on Trump instead of a good Dem candidate then this thread will continue to be very busy for many years to come.