Booker. Duckworth would be a great choice as well.
Why Booker?
Geographic diversity (west coast and east coast balance), ideological diversity (pair a Bernie wing guy with an establishment guy), demographic diversity. Also age balance is good.
Although I'll go ahead and attack my own post and mention that an all coastal ticket would be terrible for Democrats, especially in places like Wisconsin, Michigan, Minnesota, and Pennsylvania.
I think you are right about Coastal Balance (3rd Coast
) on the ticket, so I would imagine either a MidWest or Southerner would make a good choice.
Honestly, I don't think many of y'll on the Forum don't get the extent to which the stereotypes of places like New York, California, and Massachusetts are prevalent in many parts of the Country (And yes I have spent time in all three states, along with (44) other states in the US (Missing Alaska, Hawaii, and Florida)....
If Merkely were somehow to win the Dem Party nomination in 2020 (Extremely unlikely but who knows), I believe Political Geography should be the key element of selection, and then start running down the lists of the top-tier candidates within those regions....
I have no fear of Trump expanding his margins in New York State, Mass, RI, CT, CA, etc....
The reality is that he will be able to capture ME-02 (Much like Southern Oregon), hold NH, perform much better than HRC in PA.
Do Dems need to really chase the pipe dreams of AZ, GA, and even TX or let time take their course? Better to pivot hard in the MidWest and focus "on the economy stupid", slam Trump on his Achilles Heel.
Trump's appeal was ultimately based upon a half-baked vision of economic Populism, but after the toke wears off, is simply an empty high while all of us working folks are still getting paid crap wages, MNCs are still amassing major profits while we are getting laid off because of "efficiency", and meanwhile massive tax breaks for the Rich get rammed down our throats and our disabled kids and grandparents in nursing homes are virtually forced into the streets....
Better to go with a Midwestern or Southerner in 2020 once Ryan and McConnell's Dystopian dream moves increasingly closer to reality....