Rubio: I didn't get into this race to 'beat up' on rivals
© Greg Nash

Republican presidential candidate Marco RubioMarco Antonio RubioCongress faces growing health care crisis in Puerto Rico The Hill's 12:30 Report Colbert mocks Trump for sipping water during speech on Asia trip MORE on Sunday defended the timing of his attacks on rival Donald TrumpDonald John TrumpO’Malley tells Dems not to fear Trump Right way and wrong way Five things to know about the elephant trophies controversy MORE, noting he wanted to focus on the issues facing the country.

Rubio added that for much of the campaign, he's been fighting off attacks from other people.

"I didn't get into this to beat up on the other candidates," the Florida senator said on CNN"s "State of the Union" Sunday morning.

Rubio said, however, that it got to a point where he had to start fighting back.

"I can tell you that where I grew up, someone keeps punching people in the face, eventually someone's going to have to stand up and punch them back," he said.

Rubio said that if he had learned one year ago the front-runner at this stage in the Republican campaign would support Planned Parenthood and have a record of supporting government-sponsored healthcare, he wouldn't have believed it.

"I would say, 'On what planet would that be the Republican front-runner?'" Rubio said.

"But it's happened, and I think we have to ask ourselves, why have we allowed that to happen?"