With the second Republican debate on the way tonight, it’s time for another round of Donald Trump defending his position as the frontrunner. And it’s a safe bet that he’ll try to hold his ground by mercilessly insulting anyone who dares to challenge his dominance.

So let’s take a look at the insults he’s already been dishing out — and at the failed efforts by the competition to bring him down.

Donald Trump vs. Jeb Bush

Trump is a lot like a monkey who walks into a new troop, and then immediately punches the biggest monkey to become new reigning alpha. (Bear with me.) In this parable, The Donald kicked off his presidential campaign by repeatedly attacking Jeb Bush. While other candidates would have politely promoted themselves, or perhaps made oblique references to disparage Bush, Trump went directly there — and did it hard.

And since Jeb didn’t fire back — preferring perhaps to remain above the fray — he effectively forfeited the battle. His attempts to climb back so far have simply not worked — because The Donald is always ready to punch him back down again.

About two weeks ago, Jeb’s campaign tried to go after The Donald with a web video, taking on his various old liberal views:

Trump responded with a video showing Jeb lavishing warm praise on the ultimate devil figure: Hillary Clinton. And he added an extra message, “No more Clintons or Bushes!”

Trump also likes to ridicule Jeb for having no energy. Last week he posted this video, depicting Jeb as the perfect sleep aid.

Jeb tried to show off some energy — and to flaunt his Republican credentials — by opening his shirt to reveal an old Reagan/Bush ’84 campaign T-shirt.

But even in this Superman guise, Jeb still can’t bring himself to directly take on The Donald by name — with words from his own mouth. Who knows, perhaps Trump’s hair is made of kryptonite.

Advantage: Trump.

Next: Donald Trump vs. Ben Carson

Donald Trump vs. Ben Carson

Ever since he dethroned Jeb, Trump has been defending his alpha position against any challenger — by mercilessly knocking them down at the slightest provocation: Rick Perry and Lindsey Graham, for example.

But one candidate has been steadily rising up in the polls as a Trump alternative, fellow political outsider Ben Carson — who at first had resisted running any kind of negative campaign.

That changed last week, when Carson responded to a reporter’s question about Trump’s claims of devout Christian faith, by quoting the Bible: “‘By humility and the fear of the Lord are riches and honor and life.’ And that’s a very big part of who I am — humility and fear of the Lord. I don’t get that impression with him. Maybe I’m wrong, but I don’t get that impression.”

Trump hit right back, by invoking the controversy over Carson’s past involvement with medical research on aborted fetal tissue in order to impugn Carson’s own religious sincerity. And then he really went for the jugular, by attacking Carson’s single best professional accomplishment: “He was a doctor — perhaps, you know, an okay doctor by the way. You can check that out too. We’re not talking about a great — he was an okay doctor. He was just fine. And now because he’s a doctor and he hired one nurse, he’s gonna end up being the President of the United States?”

(Fact check: An accomplished neurosurgeon, Ben Carson headed up the medical team that performed the first ever successful separation of conjoined twins at the head.)

Carson then responded, not by correcting the record — but by apologizing.

“I said something that sounded like I was questioning his faith. I really wasn’t, I was really talking more about mine,” Carson told The Wall Street Journal. “But it was said in an inappropriate way, which I recognized and I apologized for that. It’s never my intention to impugn other people.”

Carson didn’t just lose this challenge to the alpha — he submitted.

Advantage: Trump.

Next: Donald Trump vs. Carly Fiorina

Donald Trump vs. Carly Fiorina

The Donald has been slamming Fiorina’s record in business for a long time. But recently he made it even more personal, in a profile piece about himself in Rolling Stone, when he remarked about her: “Look at that face. Would anyone vote for that?”

Fiorina then responded with this ad: “Ladies, look at this face!” showing the beaming visages of women who support her. But the spot had a profound bit of dishonesty: Using clips taken from Fiorina’s speech to a Republican women’s group, she boasted of how fit she was to take on sexism from the Democrats — rather than actually take on the sexism that was just directed at her by another Republican.

In a pre-debate interview with CNBC, Fiorina proudly declared that “Mr. Trump’s going to be hearing quite a lot from me.” We can’t help but wonder if she’ll grill him about how sexist the Democrats are.

Advantage: Trump, for now.

Next: Donald Trump vs. Rand Paul

Donald Trump vs. Rand Paul

For most of the race, Rand Paul has been too low in the polls for The Donald to even care about making fun of him. But it was Paul who felt the need to pick a fight last Friday, when he posted this comment after Rick Perry dropped out of the race:

The Donald’s response:

Advantage: Trump.

Next: Donald Trump vs. Bobby Jindal

Donald Trump vs. Bobby Jindal

The newest lower-tier candidate to try to punch upward at The Donald is Louisiana governor  Bobby Jindal — who isn’t even on the main stage tonight. But nevertheless, we can very likely expect that Jindal will make Trump bashing a focus of his position at the minor-league debate earlier in the evening.

Jindal began his bombardment against Trump last week, with a speech at the National Press Club and a tour of TV shows, lobbing such terms at Trump as “non-serious,” “a carnival act,” “shallow,” “full of bluster,” and “an egomaniacal, unserious person.”

Problem is, Jindal opened himself up to the question that he then had to dodge: Would he would personally vote for Trump if he won the nomination?

“We’re not gonna let him win the nomination,” Jindal said. “That’s what this is about. This is about saying — this is bigger than the Republican Party, it’s about our country.”

Trump simply responded on Twitter, by saying that Jindal doesn’t even matter:

Jindal also made a bid for chivalry and attempted to come to Carly Fiorina’s defense. “I think it’s pretty outrageous for him to be attacking anybody’s appearance when he looks like he’s got a squirrel sitting on his head,” Jindal told CBS News. “I think he should stop attacking other people’s appearances.”

Trump responded on Twitter:

Indeed, Trump is right — it is completely immature to make fun of someone based on their appearance!

But Jindal has just kept it up, when he wrote an op-ed piece Tuesday for CNN in which he sketched out the apocalyptic scenario of a Trump presidency — such as the rechristening of the presidential airplane as “Hair Force One.”

Advantage: Come on, is this one even a question?

Photo: Republican presidential candidate Donald Trump speaks at a rally in Dallas, Texas, September 14, 2015. REUTERS/Mike Stone