Told ya so. President Obama should have pulled a Joe Girardi and benched Joe Biden long ago. Hillary Rodham Clinton would have knocked last night’s debate out of the park and probably won the election for the Democrats.

Instead, Biden took the stage and made a fool of himself. The experience that supposedly qualifies him to be a heartbeat away is more than offset by the manic behavior he exhibited.

Following his mood swings was like riding a roller coaster. He was over-amped in the beginning and somber and melancholy toward the end. Did the medication kick in, or was it wearing off?

The indelible images were those numerous split screen shots of Biden laughing and shaking his head in condescension while Paul Ryan spoke about serious matters. Iran, taxes, jobs, Medicare — Biden snickered, sneered and giggled like he was privy to a private joke, while Ryan doggedly tried to address the nation’s most urgent problems.

Biden’s conduct was both rude and alarming. Instead of the services of liberal moderator Martha Raddatz, who was too deferential to Biden, we needed EMTs with a straitjacket.

Biden’s antics, including repeated interruptions, often seemed to throw Ryan off balance. But the young Republican challenger kept his cool and, while too often ceding the floor, ended up looking more mature than the incumbent 27 years his senior.

As such, he passed the most important test before him. With Mitt Romney shaking up the race with his brilliant performance in the first presidential debate, Ryan hoped to compound the gains. He may have done that in some quarters, but at the very least, he did no damage.

Centrist voters only aware of the Obama-Biden caricature of Ryan had to be impressed with his respectful and serious demeanor and firm grasp of facts on a wide range of issues, including most of the foreign- policy discussion.

He was especially good on describing the political nature of the Obama troop drawdown in Afghanistan by explaining how commanders wanted the troops there for the fighting season. Biden’s response, that politics were not involved at all is simply not believable to the many commanders who objected.

Surprisingly, Ryan left out of his answer on Syria Romney’s plan to arm the rebels, which is the major distinction from the Obama policy. He also let Biden talk too much during the tax segment and never addressed how economic growth would create jobs and help reduce the deficit.

Those moments, where Biden controlled the time and set the agenda by repeating false charges of Romney’s tax- reform plan that Ryan was forced to rebut, showed Biden at his Washington best. Arrogantly commanding the floor and talking with a certainty that belies his erratic record, he pointed his finger and even lectured Raddatz that “facts matter” when she dared challenge him.

It was pure bombast, as was his phony use of the phrase “my friend” 14 times to refer to Ryan.

To the extent that Biden’s hyper behavior was planned, it was clearly designed to reverse the image of a downcast, low-energy Obama in the first debate. Biden succeeded in that, but his conduct reinforced my concerns about his mental state. He doesn’t seem steady.

He also failed in the same way Obama did — to make a case for why the next four years would be better than the last four. That is the fundamental problem they share, and why they have turned to smear tactics to try to disqualify Romney and Ryan. That they have failed so far leaves them with a problem coming down the campaign stretch.

If they had a record they could defend, they would. And with two more presidential debates to come, Obama still must describe what a second term would look like.

If he can’t, he probably won’t get one.