'It's because he fears me' Jeb Bush explains why Donald Trump keeps going after him despite his low numbers in the polls 

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Jeb Bush again threw out a theory as to why he's become Donald Trump's favorite punching bag of the Republican field. 

'It's because he fears me,' Bush said on CBS This Morning. 'Because I'm the only guy standing up to him.' 

'And I'm doing so poor in the polls, according to everybody,' Bush chuckled, suggesting he would perform better than expected in Saturday's South Carolina Republican primary. 

On a competing morning show, Trump sniffed about Bush bringing out 'the brother,' former President George W. Bush, who participated in his first rally for Jeb Bush last night, as the former Florida governor tries to regain his footing for the White House. 

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Jeb Bush said the reason he's Donald Trump's favorite punching bag is because the GOP frontrunner 'fears' the former Florida governor 

On CBS This Morning, Jeb Bush said that Donald Trump 'kind of exploded' during Saturday night's GOP debate when the two fought about George W. Bush's record on terror 

Trump has been on a tear over George W. Bush's record in recent days. 

During Saturday night's flamethrower of a debate, Trump blasted Bush for the double sin of having 9/11 occur on his watch and then taking the country to war with Iraq. 

'The World Trade Center came down during the reign of George Bush,' Trump said at one point.  

'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,' Trump said at another. 

Trump suggested it took Jeb Bush 'five days' during the early months of his campaign to come out and say the Iraq war was a mistake. 

This morning Trump defended his attacks, suggesting to Jeb Bush that 'you can't bring out the brother' without anticipating being hit on George W. Bush's record. 

Donald Trump suggested that Jeb Bush (left) couldn't bring out 'the brother,' George W. Bush (right) without expecting to be hit on Bush 43's record, which includes 9/11 and the Iraq war 

'He might be a nice person, I don't know,' Trump said of Bush 43. 'I've never met the brother.' 

During the phone interview, with ABC News' George Stephanopoulos, Trump let up on the charge that George W. Bush lied the country into war. 

'I don't know if he lied or not, I just know there were no weapons of mass destruction,' Trump explained.  

Jeb Bush, on CBS, was incredulous that Trump, the Republican frontrunner, would attack a former Republican president. 

'He is basically mirroring the words of Michael Moore in a Republican primary,' Jeb Bush said. 'It's kind of weird. It's kind of weird altogether.' 

'I think he got angry on Saturday and just kind of exploded,' Bush added, referring to the Republicans' contentious debate. 

Bush also labeled this campaign cycle 'a little crazier' because of technology and Trump 'filling the space with vitriol and hatred and division.'

'I think he is a master at manipulation,' Bush huffed. 'And I find it amusing on one level that he constantly attacks me. I'm his primary target.'   

But with Trump being so successful at labeling Bush 'low energy' early on, host Gayle King questioned whether it might be better to turn the other cheek. 

'Yeah, I've thought that,' Bush mused. 

'And then I got back to thinking, you know what, he's hijacked my party,' Bush said. 'Someone has to take a stand.'