Sorry, I have to say it: After a mostly brilliant four days that engaged the emotions and advanced a surprising and interesting case for his reelection, Donald Trump came out and laid an egg in what may have been the worst convention speech of my lifetime.

“You may have been a headache,” Bob Hope sang in his signature tune, “but you never were a bore.” Thursday night, for the first time in memory, Donald Trump was a bore.

It’s not that he had nothing to say. He had everything to say. And he said it. And said it again. And did it in the same tone of voice. Which went like this. And then like that. And then like this again. La. Dee Dah. De Doo.

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Trump evoked every single theme of the convention and then some. The themes were good, but they were good over the four nights because they had been presented carefully and argued artfully. That was not the case for this, the most important speech of Trump’s life so far.

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There was no flow, no argument, no central core. He praised himself and he attacked Joe Biden, just as you’d expect. But he didn’t build a case for himself or a case against Biden — and it’s the construction of such cases that provide the dramatic structure a major speech needs to engage both the head and the heart.

For someone who relishes drama, Trump provided none.

Instead, we got laundry lists featuring the kinds of claimed accomplishments that are usually the province of a tiresome State of the Union address.

And when it came to going after Biden, he couldn’t find a common thread. Once again, rather than building an indictment that would then not only justify but hammer home his climactic soundbite — “You won’t be safe in Biden’s America” — he provided a dog’s breakfast.

He sought to take advantage of Biden’s quote earlier this week about how he’d lock the country down if the science said he should.

“The Biden lockdown,” Trump said, would lead to depression, not only economic but personal, in the form of addiction and suicides. “Joe Biden’s plan is not a solution for the virus, it’s a surrender to the virus,” the president said.

This is a powerful line of argument, but it requires elaboration and explanation, which he and his team likely didn’t really want to go into because it would have meant having to talk more about his response. He did talk about it, both praising himself in retrospect for having led what he called the greatest mobilization since World War II and anticipating the successful deployment of a vaccine by year’s end.

But then, just as he did in the worst weeks of April and May, he found himself stumbling in his self-justification. At one point he garbled his words and said, “Thanks to advances, we have pioneered the fatality rate” — when he wanted to say that pioneering advances have led to an 80 percent drop in the fatality rate since April.

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A convention speech watched by tens of millions is not the greatest time to slip up in this way. You don’t want your most memorable moment to be a mistake. In 1980, President Jimmy Carter never recovered from the moment in his convention speech when he referred to former Vice President Hubert Humphrey as Hubert Horatio Hornblower — a fictional sea captain.

The case against Biden then turned into a case against the radical left and the crime wave. This was the most disappointing aspect of the speech, because it’s the most important argument he can make and the one that might actually do the most damage to his rival. And here, too, he wandered all around, from public safety to statues to cancel culture.

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If you read op-eds like this one, you understood how they were connected. If you don’t, it would have seemed bewildering and disconnected.

Trump can still win this thing, without question. He just didn’t do himself any favors Thursday night, to put it mildly.

CLICK HERE TO READ THIS COLUMN IN THE NEW YORK POST