"Loyalty to country always. Loyalty to government, when it deserves it."
-- Mark Twain
In my opinion this is really not a good move, she should stay in the Senate.
First, and it's unfortunate that this is even an issue, she's a woman.
The 2020 election is probably more important than any that have come before it, so I think the Dems need to run the most straight forward (re: boring) candidates they can. Two white Christian men, one from the midwest (probably the VP) and one who's inspiring.
No Corey Booker, no Kamala Harris, no Elizabeth Warren.
Unfortunately I don't think Biden or Sanders are electable either.
So, I think it's some mix of Hickenlooper, Beto, or Michael Bennet.