Rubio: It's getting harder to stick to pledge to support Republican nominee
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Republican presidential candidate Marco RubioMarco Antonio RubioOvernight Cybersecurity: What we learned from Carter Page's House Intel testimony | House to mark up foreign intel reform law | FBI can't access Texas shooter's phone | Sessions to testify at hearing amid Russia scrutiny Cornyn: Senate GOP tax plan to be released Thursday This week: GOP seeks to advance tax overhaul 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 John TrumpDems win from coast to coast Falwell after Gillespie loss: 'DC should annex' Northern Virginia Dems see gains in Virginia's House of Delegates MORE.

"Because while I don’t want Hillary ClintonHillary Diane Rodham ClintonGOP rushes to cut ties to Moore Papadopoulos was in regular contact with Stephen Miller, helped edit Trump speech: report Bannon jokes Clinton got her ‘ass kicked’ in 2016 election 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."