Going into Joe Biden’s debate with Donald Trump on CNN, the big question was whether Biden could last 90 minutes.

We found out he couldn’t last 90 seconds.

On Thursday night everyone saw what’s left of the president’s brain and body – and it was not just a disastrous political moment for Joe Biden, it was a sad one.

It wasn’t just that his voice was hoarse at the start.

It wasn’t because of his confused and muddled answers or his five-second freeze about 13 minutes in, which he ended by uttering the mysterious words “we beat Medicare.”

It wasn’t his slack-jawed look, his vacant stare or his usual gaffes or lies about inflation or Afghanistan or his southern border policy.

It wasn’t because of CNN’s split-screen set-up. Or its moderators or their questions, which were actually pretty fair.

It wasn’t because a new and improved Donald Trump suddenly showed up to out-debate Biden with a bunch of Reagan-sharp conservative policy ideas.

Trump was the same old Trump, firing off the same messages, complaints and charges of Democrat corruption and incompetence that we’ve been hearing since 2015.

Nope. It was Joe Biden himself who was responsible for the entire disaster.

He was so awful he would have lost the debate even if Trump hadn’t shown up.

As Brit Hume wisely said afterwards on Fox, nothing either man said about inflation, the border or any other issue mattered to the millions watching.

It was simply about seeing 90 straight minutes of the real Joe Biden in action.

He had no notes with answers to pre-arranged questions. No aides whispering in his ear. No handlers to quickly escort him backstage. No media pals to edit his words or ignore his gaffes.

Over at Fox, Sean Hannity was barely exaggerating when he called Biden’s performance “the biggest trainwreck” of any presidential candidate ever.

The president’s performance was so damning, so pathetic, that Fox’s professional smart-aleck Jesse Watters said he actually felt bad for Biden.

The Democrat politicians and TV pundits who hate Trump so much that they can’t think straight – and who truly believe that Trump is Hitler 2.0 – were in shock after the debate.

CNN’s shamelessly biased White House correspondent, Jonathan Karl, who made sure to mention that Trump was “a machine gun of lies,” said what was obvious to his fellow panelists: It was a very bad night for Biden.

They could no longer kid themselves – i.e., lie to themselves – that their hero was mentally and physically capable of running for reelection (or running the country now, if they had been honest).

They could no longer pretend that in private their hero was as sharp as Maggie Thatcher, as a sad and suicidal-looking Joe Scarborough was still insisting on MSNBC Friday morning.

Former Trump White House Chief of Staff Reince Priebus told the liberals on CNN’s post-debate panel that Biden’s entire campaign was now in the toilet.

To everyone except Democrat Party groupie-for-life Donna Brazile, Biden was almost certainly done for. He was clearly not competent. But who could replace him on the ticket?

He can’t resign now because even diehard Democrats would not want VP Kamala Harris to become president for a weekend.

Would Biden accept the nomination for president at the convention and then retire and let his party come up with a new candidate who’s willing to lose to Trump?

Gavin Newsom? Gretchen Whitmer? How about the nightmare of Hillary?

Whatever bad happens to the Democrats in the fall will be well-deserved.

Biden was hung out to dry in front of millions by his party’s leaders, his Obama team handlers, and his loving wife.

They knew he was doomed to fail in a televised debate with Trump. They’ve known for years exactly how diminished Joe Biden is.

They and their partners in the liberal media have been pretending for three years that he is still the old Joe Biden.

He never was – and now the whole world knows it.

Michael Reagan, the son of President Ronald Reagan, is an author, speaker and president of the Reagan Legacy Foundation.