Republican strategist Frank Luntz on Sunday criticized Republican presidential nominee Donald Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's campaign, saying this election "should have been a slam dunk for the GOP."

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Luntz said on CBS's "Face the Nation" that Trump's campaign has been focused on the billionaire and his battles with "just about everybody."

"If he had stayed the voice and the vision for those people who have been left behind, this race would be a lot different than it is right now," he said.

Still, Luntz said he doesn't think the race is over.

He said there are enough people who are still undecided and noted Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE is under 50 percent support in many polls.

"But it requires a level of discipline that the Trump campaign has not had," he said. "This is about the voice of the voters, not the voice of Donald Trump."

Luntz continued to criticize the Trump campaign.

He said he has never seen a campaign with "less discipline" or "less focus."