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

Republican presidential candidate Marco RubioMarco Antonio RubioHillicon Valley: Supreme Court takes up Apple case | Senate votes to block ZTE deal | Officials testify on Clinton probe report | Russia's threat to undersea cables | Trump tells Pentagon to create 'space force' | FCC begins T-Mobile, Sprint deal review Feehery: Betting on Trump Senate votes to block Trump's ZTE deal MORE on Sunday defended the timing of his attacks on rival Donald TrumpDonald John Trump20 weeks out from midterms, Dems and GOP brace for surprises Sessions responds to Nazi comparisons: 'They were keeping the Jews from leaving' Kim Jong Un to visit Beijing this week 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?"