Donald Trump just couldn’t resist going after Jeb Bush during tonight’s debate over his brother George’s decision to invade Iraq after the September 11 terrorist attacks, setting up an intense argument with his nemesis that saw the entire Bush clan invoked.

‘The World Trade Center came down during the reign of George Bush,’ Trump at one point shouted.

Moderator John Dickerson tee’d Trump up for the verbal assault by asking if he still believes the ex-Republican president should have been impeached over Iraq following the discovery that the country’s dictator did not have weapons of mass destruction as the U.S. government claimed.

‘Obviously the war in Iraq is a big fat mistake,’ Trump said.

Jabbing Jeb, Trump mocked his Republican rival’s struggle last year to defend his brother’s record while admitting that the war was based on incorrect information and was therefore a mistake.

‘It took him five days, he went back – it was a mistake, it wasn’t a mistake – it took him five days before his people told him what to say and he ultimately said it was a mistake.’

Trump said, ‘Obviously it was a mistake. George Bush made a mistake, we can make mistakes, but that one was a beauty. We should have never been in Iraq. We have destabilized the Middle East.’

The leading GOP candidate was visibly and vocally incensed as he responded to Dickerson’s question about impeachment, ‘You do whatever you want, you call it whatever you want.

‘I want to tell you, they lied, they said there were weapons of mass destruction, there were none and they knew there were none. There were no weapons of mass destruction,’ he declared.

Bush demanded to respond to the assault on his family and said, ‘So here’s the deal. I’m sick and tired of Barack Obama blaming my brother for all of the problems that he’s had.

‘And frankly, I could care less about the insults that Donald Trump gives to me. It’s blood sport for him, he enjoys it and I’m glad he’s happy about it.’

The son and brother of two former presidents – George and George W. Bush – said, ‘I am sick and tired of him going after my family. My dad is the greatest man alive in my mind.

‘While Donald Trump was building a reality TV show, my brother was building a security apparatus to keep us save and I’m proud of what he did.’

Trump ferociously shouted at him, ‘The World Trade Center came down!’

Continuing, Bush said, ‘He had the gall to go after my mother. I won the lottery when I was born 63 years ago and looked up and saw my mom, my mom is the strongest woman I know.’

To which Trump told him, ‘She should be running.’

Throughout the exchange with Bush the audience booed Trump.

The battle between the two Republicans was an ongoing theme of the evening.

‘Jeb is so wrong,’ Trump declared as the foreign policy skirmish started, earning him boos. ‘That’s Jeb’s special interests and lobbyists talking,’ he said.

Trump argued again tonight that the audience was stacked in Bush’s favor because it kept shouting at him angrily and cheering the former Florida governor. It’s a complaint he made in the previous debate as well and one the Republican National Committee has denied.

Tonight he hollered back at his detractors and said, ‘I only tell the truth lobbyists.’

He was trying to respond to Bush’s assertion that he wants to ‘accommodate’ the Russians in fighting ISIS.

‘It is absolutely ludicrous to suggest that Russia could be a positive partner in this,’ Bush said.

Trump said during his turn at bat, ‘Jeb is so wrong. You got to fight ISIS first….You have to knock out ISIS. They’re chopping off heads. These are animals. You have to knock em out. You have to knock them off strong. You decide what to do after, you can’t fight two wars at one time.’

As they bickered over whether Russia should be part of the U.S.-led coalition to defeat ISIS, Bush yelled, ‘This is coming from a guy who gets his foreign policy from the shows… this is a guy who thinks that Hillary Clinton is a great negotiator in Iran.. this is a man who insults his way to the nomination.’

Later, as the topic of illegal immigration came up, Trump bashed Bush again and said he’s the ‘weakest person on this stage’ on the issue.

‘He is so weak on illegal immigration,’ he argued.

Bush snarkily interjected, ‘This is the standard operating procedure, to disparage me.’

‘It’s weak to disparage women,’ people with disabilities and to call John McCain a ‘loser’ –  ‘That is outrageous, he’s an American hero.’

Trump finally had enough and called out Bush for suggesting last week that he’d get more press if he dropped trow and ‘moon the whole crowd.’

‘Everybody would be aghast, except the press guys would never notice,’ Bush said in an interview with the Boston Globe. 

John Kasich appointed himself referee and told his fellow candidates that Hillary Clinton, the leading Democratic candidate for president, would win the general election in November if they kept it up.

After the first round of fighting between Bush and Trump the Ohio governor and surprise second-place finisher in New Hampshire, stood aghast and said, ‘I’ve got to tell you, this is just crazy, huh?’

‘This is just nuts…Jeez, oh, man, ‘ Kasich proclaimed.

The battle wounds from the evening’s skirmish won’t heal quickly. Bush said after the debate, on Fox News, that he tried to shake Trump’s hand at the end of the night and the billionaire walked away.