Former Florida Gov. Jeb Bush said Tuesday that he's under constant attack by Republican frontrunner Donald Trump because Trump is afraid of him, but that he won't ignore the attacks.

"I think he's a master at manipulation and I find it amusing at one level that he constantly attacks me. I'm his primary target and I'm doing so poor in the polls according to everybody but why is that? Why is he going after me each and every day? It's because he fears me. Because I'm the only guy standing up to him," Bush said on "CBS This Morning."

Asked whether he has thought about ignoring the businessman, who needles him on the debate stage, on Twitter, and during events, Bush said he has thought about and rejected the idea.

"I get back to thinking, 'You know what? He's hijacked my party.' I've been a conservative all my adult life and someone has to take a stand," he said.

Bush and Trump clashed during Saturday's Republican debate on CBS when Trump once again went after former President George W. Bush and called the Iraq War "a big fat mistake." He also accused the Bush administration lied about finding weapons of mass destruction in Iraq -- an idea Bush has disputed during his campaign.

"On the power of hindsight, faulty intelligence was clearly a mistake," he said. "Everybody got the same intelligence information and the great majority of people made a conclusion that he had weapons of mass destruction."

He also accused Trump of staking out an extremely liberal stance on the war, saying that he was "burying the words of Michael Moore in a Republican primary." Moore is the liberal documentary maker who made the 2004 documentary "Fahrenheit 9/11" that questioned the alleged evidence of the war.

In the lead-up to his campaign, Bush struggled to answer questions about his brother's decision making. After initially saying he would have authorized the invasion of Iraq knowing now that there were no weapons of mass destruction there, he ultimately reversed course several days later and said he would not have pursued the war.

Now Bush is embracing his brother, who found his own electoral victory in South Carolina in 2000. The former president campaigned with his brother in the state on Monday.

Bush brushed off characterizations of his brother as a person being brought in to salvage his struggling campaign.

"Those are forms of obituaries about my campaign that have been written for the last six months and I've been making slow, steady progress. My brother is my brother, I love him dearly, I'm happy that he came to campaign and the best place for him to do this," he said.

He predicted he will finish better than fifth in South Carolina, his current spot in the CBS News Battleground Tracker. He got just 6 percent among likely Republican primary voters, tying with former neurosurgeon Ben Carson.

"I'm really excited about the progress we're making. And look, I'm in it for the long haul, this is a long process. We've had three races so far, there's about 50 left and we have a national campaign," he said.