Amidst a growing list of opponents in the Republican establishment, the party's presumptive presidential nominee Donald Trump today said he does not want the support of those leaders who do not want to endorse him.

"If somebody doesn't want to endorse, I don't want their endorsement. It's OK. I'm going to release them," Trump told the ABC News in an interview, amidst reports that two former presidents – George H W Bush and George W Bush – along with two presidential aspirants Jeb Bush and Lindsay Graham have refused to endorse him.

"I understand Jeb Bush. I was rough with Jeb Bush. I think if I was Jeb Bush, I wouldn't vote for me either, if you want to know the truth, George. But they should do that. They're Republicans," he said.

The House Speaker Paul Ryan has said he is not ready to support him. The two leaders are scheduled to meet next week.

"We're going to see what happens. He wants to meet. He'd like to meet. And I think we're meeting on Thursday. And we'll just see what happens. It's just more drama," he said.

Talking about endorsements, Trump said: "I think it's a mistake not to do this. We want to bring the party together. Does the party have to be together? Does it have to be unified? I think it would be better if it were unified," Trump said in response to a question.

The real estate tycoon said he will do what he has to do to unite the party and win the November general elections.

"I'm going to do what I have to do. I have millions of people that voted for me because I want strong borders, because I want strong trade.

"I don't want to be an isolationist, but what's happening with China, what's happening with Japan, what's happening with Mexico, they're just absolutely eating our lunch. It's a shame. It's terrible," he said.

"So, I have to stay true to my principles. I'm a conservative, but don't forget, this is called the Republican Party. It's not called the Conservative Party. You know, there are Conservative Parties. This is called the Republican Party," he said.

In response to a question, Trump did not rule out raising Hillary Clinton's personal issues if her husband, the former US President Bill Clinton, gets involved in the campaign.

"I think fair game," he said, adding, "It depends on if he's (Bill) involved in the campaign. I think if he's involved in the campaign, he shouldn't be. And he probably will be involved. I think he gets involved when she plays the women card," he said.

"When she said Donald Trump was nasty to a woman, number one I've worked so well with women for so many years. I broke -- you know, you talk about the glass ceiling, what I've done in terms of jobs for women and I've gotten so much credit, and to this day I have so many women in my company that are doing so well, making so much money, I mean, in many cases making more money than men in comparable positions," he added.