They and their champion, Kamala Harris, had much to lose. Although Ms Harris has ridden a surge of support since replacing Joe Biden, she had not been tested and exposed under pressure to the wider US public.
According to most commentators and polls, Ms Harris, the presidential debate novice, was superior. Even Elon Musk said Ms Harris "exceeded most people’s expectations".
Of course, that does not an election win make. Former president Donald Trump was being himself and the race remains tight. It is the poll on November 5 that counts, not a one-off sparring session.
The biggest issue is the economy. Somehow, a majority of Americans think Mr Trump and the Republicans are stronger in this zone. Even though inflation has now fallen, unemployment rates are low and figures show continued economic success, that is not the perception.
Voter opinions count more than reality, and Mr Trump will exploit that angst far better than on Wednesday. While one poll after the debate confirmed Ms Harris as having the better of the night, 55% still said Mr Trump would be better for the economy.
She stepped out boldly towards Mr Trump to take the initiative and shake his hand. She was a little hesitant on a few earlier questions but was soon striding with poise and purpose.
Ms Harris was much more reasoned, articulate, on-topic and clearer than Mr Trump. She effectively goaded him, and she used facial expressions to project disdain and disbelief as he spoke.
Mr Trump, as expected, rambled. He made preposterous statements and was fixated on immigrants, repeating allegations about their alleged culinary tastes in residents’ cats and dogs in Springfield, Ohio.
He personally was the answer to the economy, international conflict and, of course, the border. It was weird, as Ms Harris’ running mate Tim Walz might say.
Nevertheless, he stayed in the fight. Although consistently winning on points, Ms Harris failed to deliver a knockout blow.
There was enough there for those predisposed to Mr Trump to have their views confirmed. Perhaps, also, there was as yet insufficient to sway those small numbers of crucial swing voters in those handful of swing states.
Democrats will be thrilled their candidate passed muster and then some. They should continue to be energised in their determination not only to keep the dangerous Mr Trump out but also to promote a worthy alternative.
It should be clear to New Zealanders that the Democrats are hardly on the left by international standards. While Ms Trump might have accused Ms Harris of being a Marxist and radical, these days she is in favour of fracking and much tighter border controls, and she strongly backs Israel’s rights. She responded to one of Mr Trump’s jibes by saying both she and Mr Walz owned guns.
Viewers will have noticed that Ms Harris, like Mr Trump, avoided answering some direct questions, including one early in the debate about whether Americans were better off after nearly four years of President Biden and Vice-president Harris.
The fact-check intervention from the two moderators will confirm to many that Mr Trump is correct in his claims about media bias against him.
The relieved Democrats will also be pleased Ms Harris received a second boost on the night when megastar Taylor Swift told her 283 million followers that she would be voting for Harris and Walz after watching the two candidates live and comparing "their proposed policies and plans for this country".
