These 5 picks were simply made up by a WaPo writer based on his own opinion.
1. Christie
2. Scott
3. Ernst
4. Kasich
5. Rubio
I still think the best pick is Santorum. Trump needs to shore up the Christian conservative base, and he definitely needs advice on what those constituents want to hear after his abortion/bathroom gaffes. Santorum has swing state voter appeal for PA/Ohio. He has heavy campaign experience both in the PA Senate and two Presidential primary runs, so he isn’t a newbie open to reporter ambushes. His immigration/trade message is as similar to Trump’s as almost any other potential pick. He is a “safe” pick in that he won’t have the effect of upstaging Trump on the campaign trail. He will clearly be a secondary figure to Trump in the media narrative which lets Trump stay in control of the message.
Santorum is an interesting consideration that I had not considered.