He is a Hillary stalking-horse, you know.
HMS (Her Majesty's Ship) Hillary has taken a full spread of email server torpedoes and is listing 30 degrees, belching smoke and small secondary explosions.
Droolin' Joe looks like The One, now.
A stalking horse is a figure that tests a concept with someone or mounts a challenge against someone on behalf of an anonymous third party. If the idea proves viable or popular, the anonymous figure can then declare its interest and advance the concept with little risk of failure.
What concept of Hillary's would Trump be testing?