Rubio: It's getting harder to stick to pledge to support Republican nominee
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Republican presidential candidate Marco RubioMarco RubioGOP frets over stalled agenda The Memo: GOP forms circular firing squad OPINION | Trump recertified the Iran nuclear deal — now what? MORE said on Sunday that it's getting more difficult for him to stick to the pledge he made to support the eventual Republican nominee.

"Look, I’ll be honest with you: It’s getting harder every day. It really is," the Florida senator said on ABC's "This Week" Sunday, referring to supporting front-runner Donald TrumpDonald TrumpGOP lawmaker: Trump 'is a distraction' Trump campaign paid thousands to pro-Trump TV pundit’s firm: report Intel Dem suggests Trump Jr. had more undisclosed meetings, phone calls MORE.

"Because while I don’t want Hillary ClintonHillary Rodham ClintonOPINION | Gorka: America is back with the first 6 months of Trump Poll: 1 in 8 people who voted for Trump say they wouldn't do it again Dems see huge field emerging to take on Trump MORE to be president of the United States — I do not, I want her to be defeated — I think we’re having a battle to define conservatism in the Republican Party. I do not want the Republican Party or the conservative movement to be defined by what I’m seeing out of Donald Trump’s campaign."

Rubio said he knows people are angry and frustrated, but those in positions of leadership need to show these people "a way forward that gives them hope and a belief that we can make things better.

"That's real leadership," he said.

"That’s not what we’re getting from the front-runner," he added.

Rubio said he isn't going to change his position about supporting the nominee because he still believes Trump will not secure the nomination.

"I’m going to do everything possible to keep that from happening and to give the party a choice in me," he said, "someone that people aren’t going to have to be asked that question about."