If your memory was short, you might think that some kind of self-destructive impulse had come over Donald Trump in the last couple of weeks. He held an angry press conference blasting reporters for asking questions about his charitable contributions. He attacked the judge in the fraud case over Trump University, saying repeatedly that because the judge is "Mexican" (he's actually American), he couldn't judge Trump fairly. Upon seeing a horrific massacre in Orlando, he congratulated himself for his stunning prescience in saying there would one day be another terrorist attack, then he renewed his call to ban Muslims from entering the United States and insinuated that President Obama is in cahoots with ISIS.

So now, Trump's unfavorable ratings have reached 70 percent in one poll, another shows him trailing Hillary Clinton by 12 points, and his putative allies in Congress are either condemning his latest offensive remark or scampering away in shame when reporters ask them about their presidential nominee. Has he taken leave of his senses?

Not exactly. What's going on is this: Trump doesn't understand that he isn't running in the primaries anymore.

After all, none of what Trump's doing now is really new. Outrageous attacks, bigoted statements, shocking tweets — those are the same tactics that worked so well for him during the primaries when he was only trying to appeal to committed Republicans. Indeed, there are times when he really seems not to realize it isn't still January. To this day, attendees at his rallies are likely to hear him prattle on about how great he did in various primary contests or launch into an extended criticism of Jeb Bush. It's as though he thinks that what's important is to hold on to the voters who already support him, when what he desperately needs to do is make new converts.

The same is true of his media strategy. Trump has said that he doesn't have to bother with things like having a data-driven voter contact plan, because he can just use free media to get his message to voters. After all, it worked in the primaries, right? But while monopolizing the media's attention with crazy (and frightening) rallies was a great way to crowd out his primary opponents and keep them from getting traction, he's not going to crowd out his opponent when there's only one of her. Not only that, putting a Trump rally on TV in all its spectacular vulgarity likely loses him more votes than it gains him.

And that "pivot" to the general election we were expecting? Turns out it's not happening.

When he would talk about that general election makeover in the past, Trump would say that once he dispatched his primary opponents, he'd become "presidential." But for him it was always a matter more of personal style than substance. Indeed, from what I can tell, Trump thinks being "presidential" consists solely of not insulting too many people and swearing less.

But it turned out that he wasn't even capable of that. Compared to acting like a reasonable human being, changing his positions on issues would have been a piece of cake. But he did neither. And everything he's doing now, whether it's the intensely personal attacks on Barack Obama or the ramped-up xenophobia, seems geared to the same audience and the same sentiments as when he was running in the primaries. He's not even trying to reach out to the whole Republican Party (forget about the broader electorate), just to that angry plurality that made him the nominee.

But Trump desperately needs to pivot if he has any chance to win — even if he can unite Republicans behind him. That's because there just aren't enough Republican voters to elect even a run-of-the-mill Republican as president, let alone one like Trump.

To begin with, there are simply more Democrats than Republicans in America. This difference in party affiliation isn't enormous, but it's persistent, usually around 6 or 7 percentage points in recent years. It means that even if both party's candidates do equally well in persuading their own partisans, Republicans need to either turn out their voters in higher numbers than Democrats, or persuade more of the small number of true independents to vote for them. For instance, in 2012, exit polls showed that 93 percent of Republicans voted for Mitt Romney and 92 percent of Democrats voted for Barack Obama. But because Democrats significantly outnumbered Republicans among those who went to the polls, Obama won relatively easily.

Opinions of the two parties paint an even more troubling picture for Trump. In recent polls, between 45 and 50 percent of Americans say they have a favorable view of the Democratic Party, but only around 35 percent will say they have a favorable view of the Republican Party. So Trump has to make people think better of his party, when he's doing just the opposite.

It's hard to believe there aren't people around Trump encouraging him to find ways to appeal to voters currently undecided about who they'll vote for. But something tells me he comes out of another rally every few nights — where his most committed supporters shout with glee at every insulting nickname, every rant at "political correctness," every invocation of the wall he's going to build, the people he's going to deport, the other people he's going to keep out, and the clock he'll turn back on cultural progress — and thinks to himself, "I'm killing it. This is going great. I don't need to change a thing." And there's nothing anyone can say to convince him otherwise.