Republican candidate Donald Trump says he "felt bad" after being "too rough" on Jeb Bush in his campaign announcement this week.

"I think he's a nice person. I actually felt bad because I hit him very hard one day like two days ago, three days ago, and I said, why am I hitting him so hard?" Trump told CNN's Jake Tapper in an interview set to air Sunday during "State of the Union."

Trump grilled many of his Republican competitors this week in his announcement speech, dropping the politeness and subtler digs most other politicians stick to and he delivered his sharpest hits on Bush.

"I don't see how he can get the nomination," Trump said in his kickoff. "He's weak on immigration and he supports Common Core. How the hell can you vote for this guy?"

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Trump told CNN that the Bush campaign is taking him seriously and that he knows it because "they do call, and they write, and just believe me they take me very seriously."

On reflection, the grandiose billionaire told Tapper he might have gone too far knocking Bush.

"I actually saw myself a couple of days ago and I said that's, that's too rough. Because I really think he's a nice man, I think he's a wonderful man. I don't know if I want him negotiating with ISIS. I think Trump will do a lot better. You think so too, but you're not going to say it."

Trump opened his campaign for president this past Tuesday with an hourlong speech packed with some spectacular claims, by political standards. He held out a financial statement he said showed his worth at $8.7 billion and said he "will be the greatest jobs president God ever created."

If elected president, he also said he would seek to build a wall along the border and have Mexico pay for it. (The U.S. struggled initially with the construction of the border fence, taking five years to construct from the time President George W. Bush signed the legislation creating it in 2006.)

Some top tier candidates, like Bush friend Florida Sen. Marco Rubio, have been keeping their powder dry when it comes to knocking their Republican rivals, instead focusing their fire squarely on Hillary Clinton. But Trump and a few others, including Ohio Gov. John Kasich, have had no trouble firing away at Bush.

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