Republican presidential candidate Donald TrumpDonald John TrumpGOP-Trump trade fight boils over with threat to cars Trump: Meetings on potential North Korea summit going 'very well' Freed American 'overwhelmed with gratitude' after being released from Venezuela MORE said on Sunday called politics "rough stuff," saying tactics used by his rivals are worse than the ones he faced in the real estate business.

"These people are worse than Manhattan real estate developers," he said on ABC's "This Week."

"This is rough stuff, politics."

Trump said he was hit hard on Saturday in South Carolina by two robo calls supporting rival Ted CruzRafael (Ted) Edward CruzGOP senators introduce Trump's plan to claw back billion in spending Pro-Trump super PAC raises .5 million in 6 weeks Trump has exposed Democratic hypocrisy on prison reform MORE that he called "tough and unfair."

"This is something I didn't anticipate," he said.

"So I said to myself, 'Wow, this is a tough business.'"

But Trump, who won by a large margin in the South Carolina Republican primary on Saturday, said he thought the calls and attack ads would have had a bigger effect on the outcome.

"I didn't know I was going to win by that much. And we won by a lot. You know, we won every congressional district, also we got every single delegate. So that was -- that was sort of record-setting stuff," he said.

"But they really hit me hard with negative ads."