Kamala Harris was being described by some pundits as the Democratic front-runner before she even formally announced her candidacy. By early July, she seemed poised to challenge the polling leader, Joe Biden, who she had sharply criticized in the first Democratic debate. Harris stood at 15 percent in the RealClearPolitics average of national polls, narrowly ahead of Bernie Sanders and Elizabeth Warren. Everything was coming up peaches.

Since then, however, Harris’s support has plunged. She’s down to mid-single digits in most national polls, trailing Biden, Sanders, Warren and even Pete Buttigieg. Her numbers are also dismal in the early states, Iowa, New Hampshire, Nevada and South Carolina.

So, what went wrong?

It’s too early to write Harris off; she remains well-liked by Democratic voters and has raised enough money to keep her campaign running for months. In other words, she is decently positioned to make gains if one of the top three candidates falters, or if she can create another moment, like in the first debate, that gets Democrats excited about her.

But it’s worth thinking about why Harris has stumbled from that post-first-debate high. We can’t know for sure, but here are some theories (most of these are not mutually exclusive, and many likely played a role, but I ordered them from strongest to weakest, in my view):

1. 2020 was never going to be her year in the first place

This theory views Harris’s brief rise to 15 percent in national polls as something of a fluke. Instead, Harris’s “theory of the case” was never going to truly work in 2020 — the problem isn’t Harris, really, it’s that Democratic voters are looking for something else.

At least four 2020 candidates — Beto O’Rourke, Cory Booker, Buttigieg and Harris — have run campaigns that echo Barack Obama’s 2008 run: a youthful candidate without much Washington experience runs on charisma and personality more than a defined ideology or particular policy stands. Obama is beloved by Democrats, and his 2008 campaign was iconic, so it’s natural that 2020 candidates would try to emulate him. But Harris, Booker, Buttigieg and O’Rourke are at 14 percent combined in national polls, suggesting that Democratic voters aren’t looking for an Obama re-run.

In some ways, Harris has the same problem that Ted Cruz and Marco Rubio had in the 2016 Republican primary, when they (wrongly) thought that the GOP would be excited about nominating a youngish, non-white standard-bearer with a solid conservative record.

There is evidence to support the theory that Harris just isn’t a good fit for 2020. To take just one example, Obama was 47 years old in 2008. (Harris is 54.) The three leading Democratic candidates are 78 years old (Sanders), 76 (Biden) and 70 (Warren.) Moreover, Harris’s uptick in national polls was an outlier. She was in only the high single digits for most of February, March, April, May and June, and has gradually receded back to single digits after surging in early July. Also, as mentioned, the other Obama-esque candidates aren’t really doing any better.

Even on ideological grounds, Harris has had “fit” issues. In her rise through California politics, Harris positioned herself as a left-but-not-that-left, establishment-friendly figure. But that may not be a great profile in today’s Democratic Party, which has grown increasingly liberal. Indeed, Harris has struggled to defend her sometimes more conservative decisions as a district attorney and later attorney general of California and even her choice of becoming a prosecutor in the first place. Her positioning might be just fine if Biden were not in the race winning the votes of African-Americans and Democrats to the right of Warren and Sanders, but Biden is in the race.

Speaking of …

2. Biden and Warren are just really strong candidates

OK, forget Obama, the Democratic “mood” and the type of candidate best suited to that mood. Maybe Harris’s issues have more to do with brass-tacks electioneering.

The logical path for Harris was to win with a coalition of black voters and urban, college-educated white voters. But Biden and Warren have foreclosed those paths, respectively. Biden entered the race with sky-high popularity among black voters — as Obama’s vice president, he had an eight-year head start over Harris in establishing national ties with the black community. Warren, meanwhile, has surged in the last two months. Her strategy of rolling out policy plans and taking aggressively liberal stands — such as calling for Trump’s impeachment back in April — appears to have been a shrewd one in terms of wooing white, white-collar voters. Her rise has coincided pretty perfectly with Harris’s decline.

Remember that in the run-up to the 2016 Democratic primary election, liberal activists were begging Warren to run, while the center-left of the party was urging Biden to enter the race. With strong candidates monopolizing the left and the center-left, Harris has simply been crowded out.

3. Harris has not run a good campaign

This theory takes the Harris surge in July more seriously — it was real and represented a real opportunity for the California senator. Her campaign simply squandered it.

Harris’s campaign launch speech was widely praised, and she was strong in the first debate. But she has not had a strategy of keeping herself in the news, the way Warren’s policy rollouts and liberal stances did earlier in the year. And Harris hasn’t built a clear brand and rationale for her candidacy along the lines of Buttigieg’s (“I’m young”), Biden’s (“I can beat Trump”), or Sanders and Warren (“I will take on the wealthy”).

I think this lack of clarity about the rationale for her candidacy — beyond appealing to a broad coalition of Democrats — has led to some of Harris’s stumbles. Her months-long waffling on Medicare for All likely stemmed from a desire to appease both the party’s left-wing (which favors MFA) and the center-left wing (which opposes MFA). But this field may be too big for anyone to straddle the left and center-left — and perhaps health care is an issue where you can’t equivocate. Similarly, while Harris attacked Biden’s past opposition to aggressive school integration plans, she was hesitant to offer much of a proposal of her own on that issue. It seemed like Harris wanted to use that issue to nod at her racial liberalism but wasn’t prepared to commit to a big school integration plan, which might be controversial.

4. She’s a woman of color in a party wary of nominating someone who it feels won’t connect with white voters in the Midwest in the general election

“Electability” has been a bigger issue for Democrats in 2020 than perhaps any presidential primary in modern history. Democrats want to beat Trump. And in the wake of his Electoral College win in 2016, many Democratic voters are concerned about winning over white swing voters, especially in the Midwest. Perhaps not coincidentally, Biden is viewed as the most electable — maybe because of his more moderate stances and vast political experience, but also maybe because he’s white and a man.

If Biden and Sanders and O’Rourke were the three leading candidates, I would have argued that this was Harris’s biggest barrier — Democratic voters are behaving like pundits and determining that only a white man can win the general election. But Warren’s rise at least suggests that many Democrats are open to nominating a woman.

Still, that doesn’t mean that this isn’t an issue for Harris’s campaign. Being a woman of color — Harris is the daughter of Jamaican and Indian immigrants — may be a bigger barrier than being a white woman. Why? Well, Harris’s strategy, more than Warren’s, depends on her doing really well with black voters. (I’m not saying this just because Harris is black, her campaign has made a strong showing in heavily black South Carolina a focal point.) It may be extra hard to succeed if you are black woman trying to win over black Democrats, many of whom feel like America embraced Trump as part of a racist backlash against Obama. Black voters in particular may like Harris but truly feel that Biden is much more likely to win a general election.

Here’s the thing: I don’t think Harris is out of this race. She has a clear and kind of obvious path back into the top tier if she can just win over some of the people who are now behind Biden (particularly black voters), Warren (college-educated whites) and the other candidates who are of her general ilk (Julián Castro, Booker, Buttigieg and O’Rourke have a combined 10 percent of the vote.) It’s entirely possible that in December or January, Democrats feel like Biden is not inspiring enough but also that Sanders and Warren have taken too many left-wing positions and are risky bets in the general. In such a scenario, Harris, along with Buttigieg, are the best positioned candidates to rise.

But a lot would have to happen for Harris to pull off such a comeback. Right now, she seems more likely to finish behind Andrew Yang than to win the Democratic nomination. That’s pretty stunning, and makes me think that perhaps all four of these things are happening at once. Maybe the best explanation for Harris’s struggles is that she hasn’t been a great candidate and also faced three things that were out of her control: the strong performances of Biden and Warren, doubts from some Democrats about a woman of color’s ability to win the general election and a Democratic electorate looking for either a really leftward shift (Warren, Sanders) or someone decidedly against that shift (Biden.)