1. Elizabeth Warren: Warren will be one of the prime movers in the 2020 election. She will decide whether she wants to run, and then lots of other people — including many below her on this list — will make their own plans accordingly. What Warren has that no one else does: A nationally known name, a massive fundraising base and a demonstrated liberal record. Lots of liberals wanted her to primary Hillary Clinton in 2016, but Warren passed, leaving the door open to the surprising success of Bernie Sanders, who ran on, essentially, Warren's message. Warren would be 71 on election day 2020, but Trump would be 74, taking age entirely off the table as an issue.
2. Kirstin Gillibrand: I wrote in my book, which of course you read, that the New York senator might be the person best positioned to pick up the mantle left by Clinton. (I was talking about 2016, not 2020, but never you mind!) Gillibrand was appointed to Clinton's Senate seat in 2009 and has subsequently won reelection easily, proving in the process that she is one of the best fundraisers in the party. Gillibrand has also moved hard to the left since her days as a centrist Upstate New York member of the U.S. House.
3. Kamala Harris: The newly minted California senator will have a quick turnaround time to decide whether she runs for president. She'll have spent only two years in the Senate when a go/no-go decision will become necessary following the 2018 election. If Harris wants to run, she would be formidable — a California fundraising and activist base coupled with her historic status in the party (she's only the second African American female senator and the first Indian American) make her uniquely appealing. And remember that Barack Obama was elected to the Senate in 2004 and ran for president in 2008 — the same timetable Harris would be on.
4. Amy Klobuchar: Klobuchar has the right sort of resume — former county prosecutor, two-term senator — to run for president. And she's from the Midwest, the part of the country where the presidency was lost last November. The question for Klobuchar is whether she could compete financially and in terms of profile with some of the bigger names on this list and in the race (Cory Booker, etc.) more generally. She's also up for reelection in 2018, a race she should win, but that could take time, energy and money away from planning a 2020 bid.
5. Tulsi Gabbard: The Hawaii congresswoman made waves (Ugh. I'll show myself out.) during the 2016 primary race when she emerged as a strong backer of Sanders. Her decision to resign as a vice chair of the Democratic National Committee looks brilliant in hindsight given how the DNC became the symbol of many liberals' issues with the Democratic Party. For all of Gabbard's potential, however, a run for president would be a major leap. The history of House members running for president isn't overfilled with success stories. And, at 35 years old, Gabbard can afford to bide her time.
6. (tie) Tammy Baldwin and Claire McCaskill: Baldwin, a Wisconsin senator, and McCaskill, a Missouri senator, could both be intriguing national candidates — albeit from different ideological perspectives (Baldwin is more liberal, McCaskill more conservative). The issue for both is that they face reelection races that could be problematic. McCaskill will be a major Republican target in a state that Trump won by 18 points in 2016. And Baldwin watched as Wisconsin reelected Sen. Ron Johnson (R) in 2016 despite widespread expectations that former senator Russ Feingold (D) would win. Neither woman will be able to take their eyes off their reelection races, making it harder to plan for a 2020 bid.
8. Maggie Hassan: The newly elected senator from New Hampshire ran a terrific campaign against incumbent Kelly Ayotte (R), herself someone regularly mentioned for higher office. Hassan's problem isn't necessarily timing — she'd be on the same four-year pivot as Harris — it's the fact that being from a small northeastern state can be a significant hindrance to winning a presidential nomination. Raising money for Hassan would be very tough, and, if she did run, her opponents would likely back out of the New Hampshire primary, giving her a hollow victory along the lines of Tom Harkin in Iowa in 1992.
9. Tammy Duckworth: The Illinois senator's personal story — she lost both of her legs while serving in Iraq — is compelling and powerful. Like President Obama, she would benefit from her roots in a state with a very strong Democratic tradition and a solid fundraising base. But Duckworth seems much more likely to work her way up the Senate leadership ladder than take a flier on national office.
10. Val Demings: You've probably never heard of Demings. So, how does she make Davidson's (and therefore my) list? She's the former Orlando police chief and now a freshman member of Congress. She's also an African American woman. Demings is impressive, and you can bet Democrats will look for every opportunity to push her into the national spotlight. But see my point above regarding Gabbard: It's VERY hard to run a serious presidential race from the U.S. House.
11. Sheryl Sandberg: In this outsider political environment, Sandberg could be tremendously appealing. Her high perch at Facebook, her fame from her "Lean In" book and her personal wealth mean that she would immediately be a player in the 2020 field. The only issue? Sandberg, unlike some other wealthy business executives (Mark Cuban, Howard Schultz, Tom Steyer), seems uninterested in running for office.