With the start of voting in presidential primaries just a little over two weeks away, six Democratic candidates for the top job took the stage at Drake University in Iowa.

Here are the key takeaways from the final debate before the first votes of the 2020 elections are cast:

1. Sanders vs Warren

After a weekend of leaked comments and accusations, everyone was expecting a huge clash on stage.

And it *kind of* delivered, but it took the moderators prompting the pair to fight over Senator Sanders' alleged comments to Senator Warren that a woman couldn't win in 2020.

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Just after this exchange Senator Warren tried to trip Senator Sanders up on a semantic point, which is the kind of tactic you'd expect her to roll out for her moderate rivals (or President Trump) rather than her progressive ones.

More fascinating was this moment just after the debate ended:

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This was real animosity, and there are hundreds of journalists trying to figure out what was said between the pair right this second. Given the turn the campaign has taken, it'll probably leak before too long.

This debate may not have ratcheted up the tension, but it made it clear that the implied non-aggression pact between the two campaigns is over.

2. Elizabeth Warren had a good night, is it enough?

Can Elizabeth Warren's debate performance give her a boost in Iowa? ( Reuters: Shannon Stapleton )

For one, she had the most speaking time. And just like previous debates, she made good use of it.

Senator Sanders (who had been enjoying a moment as a potential frontrunner) took most of the heat for the progressive case this time around, which meant Senator Warren was on the front foot for most of the debate.

Her line comparing the elections the men and women on the stage had won got the biggest cheers:

"Can a woman beat Donald Trump? Look at the men on this stage. Collectively, they have lost 10 elections. The only people on this stage who have won every single election that they've been in are the women," she said.

Plenty of Democratic voters are about to ask that question themselves when the primary season begins — can anyone other than a moderate white man defeat Donald Trump in the general election?

Senators Warren and Klobuchar are rightly confident in their impressive resumes.

But the makeup of the stage tonight — majority male, majority moderate, 100 per cent white — might suggest that voters, rightly or wrongly, are closer to making their minds up than we think.

3. We wanted spice… but for most of it we got mayonnaise

Imagine tonight was a pool party, with Joe Biden and Bernie Sanders bobbing about on a couple of pool noodles taking a nap, ripe for the dunking.

Elizabeth Warren dipped a toe in the water, but backed out. Pete Buttigieg, Amy Klobuchar and Tom Steyer all stayed inside the house with their suits on talking about the weather.

Tonight was *the* night for these candidates to come out swinging … and they just didn't. The moment everyone will be talking about happened after the debate finished.

The handshake that wasn't. ( Reuters: Shannon Stapleton )

Senator Sanders copped more flak from the moderators than his rivals. And once again Mr Biden seemed content to fly under the radar and hope no-one realises he's been the frontrunner since he joined the race.

The moderators deployed a good line of questioning by asking everyone about their biggest perceived weaknesses, but it's telling that this late into the race the heat didn't come from the candidates themselves.

Whoever wins will be up against a president who won't hesitate to go after them where it hurts most. The time to play nice is rapidly coming to a close.

4. Iowa is wide open. The national race probably isn't

A good chunk of these candidates could win in Iowa. A good chunk of them have almost no chance of winning the nomination too. ( Reuters: Shannon Stapleton )

In 20 days, the first votes in the 2020 presidential primary will be cast.

And nothing that happened tonight looks likely to shake up a race in Iowa that looks wide open for the top four candidates.

But Iowa isn't the broader Democratic Party. When FiveThirtyEight reordered the primary calendar so the states that best reflected the make-up of the Democratic electorate voted first, Iowa ranked 42nd.

It's most likely why Joe Biden decided to play it safe in this debate, confident in the knowledge that he holds significant leads in plenty of the states that vote after Iowa.

A loss in Iowa would generate some bad headlines for the former vice-president, sure. But the fact remains that everyone else needs victories in these early states to keep their campaigns alive deep into the primary season.

Catch up on how the debate unfolded in our blog below: