Donald Trump won the Democratic debate last night.

He wasn’t actually there, obviously.

But he’ll have been sitting in his private quarters at the White House chuckling at what he was watching.

In fact, he was enjoying it so much he didn’t even bother tweeting his usual real-time derision. Perhaps he felt the candidates were damaging themselves enough without needing any help from him?

For the cold, harsh reality is that right now, none of these Democrat contenders look anywhere near like beating Trump in 2020.

Joe Biden is the clear front-runner, and was the primary target for friendly fire attack last night, but he’s looking and sounding his age, and that’s a massive problem for the party that wants to regain power next year.

Joe Biden is the clear front-runner, but he’s looking and sounding his age, and that’s a massive problem for the Democrats

Biden’s now 76, will be 77 in November, and 78 when he takes office if he wins the presidency.

That would make him the oldest president ever elected to a first term.

And whilst I share the widely held view that Biden is a thoroughly decent, intelligent man with decades of Washington experience behind him, there’s a very fine line between ‘reassuringly experienced’, and ‘over the hill’ electoral road-kill – and he’s in serious danger of crossing it.

The killer moment last night for me was Julian Castro, 44, openly mocking Biden for his recent spate of embarrassing public forgetfulness.

‘Are you forgetting what you said two minutes ago?’ Castro taunted, as Biden struggled to articulate his healthcare plan.

The killer moment last night was Julian Castro, 44, above right, openly mocking Biden

It was a brutal jibe, and exposed Biden’s biggest weakness – his apparent age-related mental fragility.

Nor did I think his response was very good.

‘I’m fulfilling the legacy of Barack Obama and you’re not,’ Biden sniped back at Castro.

It was one of many times he’s invoked Obama’s name during the debates, and it’s a dangerous strategy.

Biden’s nothing like Obama, in style, rhetoric or, especially, youthful vigor, and constantly reminding everyone of that may turn out to be an act of massive self-harm.

Biden’s nothing like Obama, in style, rhetoric or, especially, youthful vigor, and constantly reminding everyone of that may turn out to be an act of massive self-harm.

Later in the debate, in a strangely incoherent and rambling response to a question about his record on race, Biden urged viewers to ‘make sure that you have the record player on at night’ for kids.

Sorry, what?

I’m 54 and even I barely remember what a ‘record player’ is.

He may as well have put on a pipe and slippers and purred about his ‘Gramophone’.

Biden then inadvertently called Bernie Sanders ‘President’, just as he had wrongly promoted Cory Booker to the White House in a previous debate.

It’s a dumb mistake to make once, but it’s a worrying pattern to then do it again.

And in yet another awkward moment that quickly went viral on social media, Biden began gurning in a very weird way that looked like his dentures were breaking out of his mouth.

This followed one of his eyes going bright red during CNN’s climate change debate last week after a blood vessel broke - which is usually a sign of stress.

Biden inadvertently called Bernie Sanders, right, ‘President’, just as he had wrongly promoted Cory Booker, left, to the White House in a previous debate

And it also followed a string of other damaging missteps he’s made since announcing he was running - including confusing New Hampshire with Vermont, saying Bobby Kennedy and Martin Luther King were assassinated in the late ‘70s, and recounting a story about a military ceremony in which he got almost every detail wrong

None of this in isolation would be particularly problematic, but when you put it all together, it adds up to a growing sense that Biden’s losing it.

‘I’m not going nuts!’ he insisted to Stephen Colbert last week, in an appearance designed to quell the rumors that he is indeed going nuts.

‘I’m not going nuts!’ he insisted to Stephen Colbert last week (above) in an appearance designed to quell the rumors that he is indeed going nuts

Perhaps not, but is he, like many people in their late 70s, going slightly senile?

That is the urgent question dogging Democrats today.

And it’s one Biden needs to counter strongly and competently, without spilling more fuel on the feeble fire.

But if I were the Democrats, what would concern me even more than Biden’s rather dithering performances would be his inability to excite an audience.

Trump, love him or hate him, can whip up a crowd like few in modern American political history.

You don’t have to agree with what he’s saying to acknowledge his bombastic, dynamic, rabble-rousing communication skills.

Trump’s a brilliant marketer, and as he showed in 2015-16, also a ruthless campaigner and rally-master.

He knows his base, he knows how to wow them, and he’s kept them at an unwaveringly fervent and consistent level of support ever since he won.

If Biden’s the Democrat nominee, as seems increasingly likely, he needs to motivate HIS support to come out and vote for him.

And right now, he’s not showing anything like the fire that I think the Democrats need to win.

The reason for that may be as simple as the unsalvageable onset of old age.

Biden just doesn’t look as physically or mentally lively as he was even four years ago, when I thought he should have run and when - as I wrote at the time - I genuinely thought he’d have had a better chance of winning than Hillary.

Of course, Trump himself is no spring chicken and would be 74 on Election Day.

But for all his often bizarre and erratic antics, there’s clearly no issue with the President’s energy levels.

And he’ll be coming at whoever ends up facing him in 2020 with the force and volatility of an enraged two-ton bison with a spear in its back.

That’s why Donald Trump was the real winner last night.

Trump himself is no spring chicken and would be 74 on Election Day. But for all his often bizarre and erratic antics, there’s clearly no issue with the President’s energy levels

He knows that Joe Biden’s likely to be his opponent next year, and he also knows that Joe Biden’s already struggling with the pace of this race.

Trump is adept at seizing on an individual’s weakness, and exploiting it for his own gain.

He reveled in Hillary’s health issues towards the end of the last campaign, not least when she keeled over getting into a car, and right now, he’s licking his lips with glee at what he’s seeing.

Hillary made headlines when she collapsed at the 9/11 memorial in 2016 while running for president (moment of collapse pictured above)

The challenge for the Democrats, and for Joe Biden, is how to energize themselves enough to combat a rampaging political beast intent on giving them another humiliating kicking at the ballot box.

At the moment, it just isn’t happening.

And if they don’t fix that very soon, Trump’s getting re-elected.