The Washington PostDemocracy Dies in Darkness

Who are the late-arriving Hillary Clinton challengers? We ranked them.

Sen. Elizabeth Warren (D-Mass.) speaks at the Phoenix Convention Center during the Netroots Nation convention July 17. (Cheryl Evans/Arizona Republic via AP)

Hillary Clinton's ongoing struggles to effectively deal with questions surrounding her use of a private e-mail server while at the State Department have stirred talk that it's still not too late for a candidate to swoop in and take the nomination from her.

I'm on the record as skeptical about that possibility, largely because it is very close to too late when it comes to the massive fundraising and organizational lift a presidential race requires. And because Clinton's numbers remain quite strong among Democrats.

Of course, those facts won't stop the speculation about who might run -- and whether he/she could beat Clinton. So I thought it made sense to rank the most-commonly mentioned names by the threat they pose to Clinton's chances at the nomination. Those rankings are below. Let me emphasize: I don't expect any of these candidates to run (although I have no clue where Joe Biden's head is right now). But, if they did run, here's how problematic each would be for Clinton.

5. Al Gore: Um, no.  The former vice president hasn't run for anything in 15 years.  Neither he nor the public seem particularly upset by that fact.

4. John Kerry: Having run for president before is often a very good indicator of wanting to run again. And there's no doubt that the senator-turned-secretary-of-state has regrets about the way he ran in 2004 against George W. Bush. But if Kerry couldn't be president, his current gig as the nation's top diplomat is clearly his second-choice job. He relishes the world-hopping nature of the job and probably wants to do everything he can to shepherd the Iran deal he negotiated to a successful conclusion. Plus, I don't get the sense the Democratic Party is clamoring for another Kerry candidacy.

3. Joe Biden: The only person on this list who actually might run, the vice president clearly has a group of loyalists -- staff and voters -- who will be for him if he gets in. But how big is that group? In most recent polling on the race, Biden is in low double digits -- running well behind Clinton and Sanders. Yes, his numbers would probably move up in the aftermath of a presidential announcement. But it's still hard for me to see how he differentiates himself from Clinton enough to beat her. Biden is a more gifted natural campaigner than Clinton, but there's almost no other measure where he is her superior. The biggest beneficiary of a Biden candidacy would be Sanders because it would lower the percentage of the vote he would need in Iowa, New Hampshire and beyond to win.

2. Billionaire outsider: The Howard Schultz bubble appears to have burst. But someone with a profile like the Starbucks chief executive -- very rich, liberal, never before involved in politics -- could be very appealing for voters looking for something totally different. The remarkable success of Donald Trump on the Republican side suggests that people are desperately in search of anti-politicians. Why does that person need to be rich, too? To pose a real threat to Clinton, you would need someone with the ability to write a $50 million check to his/her campaign to fund efforts to qualify for early state ballots, pay staff and run TV ads.

1. Elizabeth Warren: What the success of Bernie Sanders's candidacy has proven is that (a) the liberal, populist base of the Democratic Party is desperately searching for an alternative to Clinton and (b) there are lots of people in that base. Sanders has ably filled the void left by Warren, but if the senator from Massachusetts were to reconsider the race, she would almost certainly push Sanders to the sidelines (or out of the race entirely) and immediately become a major threat to Clinton. Warren still represents the populist heart of the Democratic Party. Clinton still represents its pragmatic head. And heart almost always wins in primary fights.