5 key takeaways from the Democratic debate: The major battle lines of night 1

For some on stage, this debate may be their last national audience.

Senators Bernie Sanders, I-Vt. and Elizabeth Warren, D-Mass., the two highest-polling candidates at center stage tonight, both forcefully defended their policy agendas from frequent attacks from candidates like former Maryland Rep. John Delaney, Montana Go. Steve Bullock and Ohio Rep. Tim Ryan. A major point of contention between the candidates was an issue that continues to take center stage during the Democratic primary: health care.

Tuesday night was also seen as the last best chance for the moderate candidates, many of whom are mired towards the bottom of the pack in terms of polling and fundraising, to get their message out to a national audience before the Democratic National Committee imposes stricter rules to qualify for the debates in September and October.

Beyond the policy discussions, candidates also took aim at President Donald Trump and congressional Republicans, all hoping to earn the chance to deny him a second term in the Oval Office.

Here are five takeaways from night one of the second Democratic primary debate.

Warren, Sanders defend the progressive agenda

Much was made about Warren and Sanders, two of the most visible leaders of the modern progressive movement, taking center stage on Tuesday night, and sure enough a consistent theme Tuesday night was their defense of that movement’s agenda.

Amid frequent attacks on their policy prescriptions and visions Sanders and Warren remained steadfast in the face of criticism that their ideas are unrealistic or impractical.

"You can't just spring a plan on the world and expect it to succeed," Hickenlooper said during a back-and-forth with Sanders on health care.

"I get a little bit tired of Democrats afraid of big ideas," Sanders said later responding to an attack from Delaney on "Medicare for All."

"I don't understand why anybody goes to all the trouble of running for the President of the United States to talk about what we really can't do and shouldn't fight for," Warren, who frequently clashed with more moderate candidates, said in another response to the former Maryland congressman who said her and Sanders' agenda is anti-private sector.

Despite the constant contrasting, neither Sanders nor Warren or anyone on the debate stage Tuesday said the name of the candidate currently leading the pack in polling: former Vice President Joe Biden.

Health care takes center stage once again

Democrats made health care a centerpiece of their successful campaign to re-take the U.S. House in 2018, and once again the issue continues to dominate the debating heading into 2020.

Roughly the first 30 minutes of Tuesday night's debate were dominated by one subject: health care. More specifically it was about one policy, Medicare for All, which remains a dividing line among the Democratic contenders.

Sanders and Warren both vociferously defended Medicare for All from attacks from multiple candidates, including from both a clearly aggressive Delaney and an eager Tim Ryan.

"I wrote the damn bill!" Sanders said when Ryan challenged him on the specifics of what would be covered in his Medicare for All plan.

O'Rourke, Buttigieg and others tried to make the pitch that America will eventually transition towards a Medicare for All system by offering a public option to compete against private health insurance.

The former Texas congressman also pledged that middle-class taxes will not be increased under his healthcare plan, a point of contention and disagreement among those pitching Medicare for All.

Moderates try to make their mark, maybe for the last time

Tuesday was also billed as the last best chance for candidates mired towards the bottom of the polls to break out before the DNC imposes stricter debate rules for the fall.

That urgency was evident for candidates like Bullock, Delaney and Hickenlooper, who each repeatedly tried to pitch a broader and more succinct argument for why they’re the best candidate to unite the party and defeat Trump.

"I'm running for president to beat Donald Trump, win back the places we lost, and make sure that Americans know that where Washington’s left them behind in the economy and political system, I'll be there," Bullock, who was appearing on the debate stage for the first time, said in his closing statement.

"I have actually got a track record as a small business owner, as a mayor and as a governor," Hickenlooper argued.

The effects of their performance won't be fully known for a few days or weeks, but many of these candidates may have to face the reality that this was their last chance to stand toe-to-toe on a national stage with their fellow Democratic contenders and make their pitch.

Candidates address Trump, recent racial controversies head on

Not surprisingly many candidates took time on the debate stage to directly call out President Trump in concise and stark terms.

"The racism, the bigotry, and the entire conversation that we're having here tonight, if you think any of this wonkiness is going to deal with this dark psychic force of the collectivized hatred that this president is bringing up in this country, then I'm afraid that the Democrats are going to see some very dark days," said author Marianne Williamson, who had a few standout moments Tuesday evening.

"We need to call out white supremacy for what it is, domestic terrorism. And it poses a threat to the United States of America," Warren said in response to a question from CNN's Don Lemon about President Trump running a re-election strategy based on "racial division."

Both Williamson and O'Rourke brought up the idea of reparations for the descendants of slaves.

"The legacy of slavery and segregation and Jim Crow and suppression is alive and well in every aspect of the economy and in the country," the former Texas Congressman said, also pledging to enact a bill to study reparations authored by Texas Democratic Rep. Sheila Jackson Lee.

O'Rourke tries to regain his footing, Buttigieg takes aim at Trump, GOP

O'Rourke faced lofty expectations when he got in the race back in March after his electrifying run for the U.S. Senate in 2018, and thus far has struggled to deliver. Prior to Tuesday, he made it clear that this debate was an opportunity to regain his footing and boost himself back into the discussion as a legitimate contender for the nomination.

On Tuesday the candidate was prepared for a question on decriminalizing crossings at the U.S.-Mexico border, a topic that tripped him up during last month's debate. The candidate also brought the focus to his home state of Texas, which will be critical to his chances of clinching enough delegates to capture the Democratic nomination.

"Bernie [Sanders] was talking about battleground states in which we compete. There's a new battleground state, Texas, and it has 38 electoral college votes," O'Rourke said to applause and agreement from the crowd his fellow candidates.

Buttigieg, who has arguably been on an opposite trajectory from O'Rourke, leading the pack in fundraising in the second quarter, unleashed sharp attacks on Trump and Republicans in Congress.

"if you are watching this at home and you are a Republican member of congress, consider the fact that when the sun sets on your career, and they are writing your story of all the good and bad things you did in your life, the thing you will be remembered for is whether in this moment with this president you found the courage to stand up to him, or you continue to put party over country," Buttigieg said in one of the night's most memorable moments.

O'Rourke and Buttigieg are both running as aspirational candidates of generational change, and the competition for voters looking for just that type of candidate likely won't get any easier after Tuesday's debate.