The presumptive GOP nominee also warned that Republicans still wary of his candidacy need to get "tough" and "smart" or risk losing their re-election battles, which Trump said could topple the Republican majority in the Senate.
"I mean, I've had more opposition from the Republican Party than I do from the Democrats," Trump said during a rally here, drawing boos from the crowd. "The Republican Party has to be tough and has to be smart. And if they're not tough and smart, I'm going to win, but a lot of other people won't."
Trump projected Republican unity -- at least at the state level -- at his rally as Florida Attorney General Pam Bondi and Gov. Rick Scott, both Republicans, revved up the crowd before Trump took the stage.
Trump warned that losing control of the Senate would be "bad" and urged Republicans to "stick together" to prevent that outcome. Democrats, Trump argued, "to a much greater degree, they stick together."
But even as he bemoaned the lack of Republican unity, Trump continued to level attacks against other Republicans, most notably former Republican nominee Mitt Romney, who on Friday told CNN's Wolf Blitzer that a Trump presidency could lead to "trickle-down racism"
and "trickle-down misogyny."
Trump rallied his supporters against Romney on Saturday, telling them Romney "choked and he let us down."
"The guy is a stone-cold loser," Trump said.
Trump has endured a sustained barrage of criticism from his fellow Republicans since he accused a U.S. federal judge of being biased against him because of his Mexican heritage. The judge, who was born in Indiana, is presiding over a case against Trump's scandal-ridden Trump University project.
House Speaker Paul Ryan called Trump's remarks about the judge "the textbook definition of a racist comment."
Others, including Senate Majority Leader Mitch McConnell, called Trump's comments wrong and inappropriate.
Trump has refused to apologize for his comments about the judge, saying instead that his comments were "misconstrued"
and insisting in recent days that he is the "least racist person there is."
Still, Trump appeared on Saturday to chalk up Republicans' rebuke to political correctness.
"We have to get smart. We have to get tough. We have to stop being so politically correct," Trump said. "The Republican Party and our leaders, we've got to get down to business."