On a clear evening before his campaign, Trump conjures up another dark vision

Despite dominating the Super Tuesday nominating contests, former President Donald J. Trump delivered a victory speech with little celebration or elation and long with sinister evocations of what he portrayed as a grim fate for the country if President Biden is re-elected.

“We have seen our country take a huge hit over the last three years,” Trump told supporters Tuesday night at Mar-a-Lago, his private club and residence in Palm Beach, Florida. “And no one thought anything about it. as if this were possible.”

He made no mention of his only Republican rival, Nikki Haley, his former ambassador to the United Nations, whose victory in the Vermont primary — the first state she captured — was declared by The Associated Press just as he finished speak.

A somber Mr. Trump recited a familiar list of grievances, emphasizing that the nation was sliding toward chaos under Mr. Biden’s leadership and raising questions about election integrity even as he has sailed through the Republican primaries.

“We are a third world country at our borders, and we are a third world country in our elections,” Trump said.

His speech was yet another signal that he has turned his attention to the general election and an increasingly likely contest against Mr. Biden.

Mr. Trump claimed, as he often does, that foreign policy crises in Ukraine and Gaza would have been averted if he had only won in 2020.

And he again characterized the migrants streaming across the country’s southern border at record levels as part of an “invasion,” painting them broadly as violent criminals and murderers.

Border authorities who worked for the former president have said most people crossing the border are vulnerable families fleeing poverty and violence.

Trump gave a brief nod to his victories, calling Tuesday a “great day” and thanking his family and campaign staff.

Even as Ms. Haley won Vermont and made strong showings in several states that indicate a faction of Republicans remains opposed to his candidacy, Mr. Trump insisted the party would rally behind him.

His success, he said, would “ultimately unite this country and this party.”