The Republican presidential frontrunner warned Iowans Tuesday that “the American dream is dead” and “the world is in flames,” as he raised the specter of a global nuclear conflict that will result in complete “obliteration.”

Former President Donald Trump, who has a commanding leading in the polls just five weeks before the Iowa caucuses, also doubled down on his recent controversial public comments suggesting that the “blood of our nation” is being destroyed by immigrants.

He did not mention Tuesday’s decision by the Colorado Supreme Court to block him from the ballot in that state under a Civil War-era “insurrection clause,” based on his actions related to the Jan. 6, 2021 attack on the U.S. Capitol.

Speaking in Waterloo to a crowd of supporters that included Iowa Attorney General Brenna Bird, Trump said that while the threat of World War III — he didn’t specify the combatants or the cause of the conflict – is imminent, he alone has the power to pull the world back from the brink of destruction.

“I’m the only candidate, and I think you know this, that can make this very important promise,” he said. “I think the world is in more danger than it’s ever been because of the power of weaponry, and I will be the only one that can say this with great surety: I will prevent World War III. World War III, we’re very close. I don’t know if you feel it. I don’t know, madam attorney general, if you feel it, but we’re very close to World War III when you see these discussions taking place.”

Throughout his hour-long speech, Trump credited himself for rebuilding the military to “tippy top” condition, saving the ethanol industry in Iowa, and restoring the ability of people to wish each other “Merry Christmas.” He also reiterated his disproven claim that the 2020 election was “rigged.”

In the process, he described America as a country that has “gone to hell” and as “a nation in decline,” which he blamed on the policies of Democrats and the Biden administration.

“With your vote in this election, together we’re going to save America and we’re going to bring our country back from hell,” he said. “As long as Joe Biden is in the White House, the American dream is dead. There is no American dream. But all of that will change the minute the polls close on Election Night in 2024. It’s gonna all change.”

He said that “by Christmas next year” – which would predate his taking office, should he win the general election – “the economy will be roaring back, energy prices will be plummeting and the hordes of people charging across our border will have totally ended and the invasion will have stopped.”

The crowd seemed most appreciative of Trump’s comments on illegal immigration, which lately have drawn criticism, even from GOP leaders, who say his rhetoric echoes that of Adolf Hitler in the German dictator’s manifesto, “Mein Kampf.” In his book, Hitler characterized immigration and the mixing of races as “blood poisoning,” which is the same phrase Trump used recently in a New Hampshire speech.

“We have no idea who any of them are,” Trump said of the immigrants entering the United States. “They come from Africa. They come from Asia. They come from South America. But not just South America. All over the world. They dump them on the border, and they pour into our country … They are ruining our country. And it’s true: They are destroying the blood of our country. They’re destroying our country. They don’t like it when I said that  — and I never read ‘Mein Kampf.’ They said, ‘Oh, Hitler said that’ – in a much different way.”

He said immigrants now entering the United States “could be very unhealthy, they could bring in disease that’s gonna catch on in our country, but they do bring in crime… We’re gonna have to get them out. We’re gonna have to get mass numbers of these – especially the criminals. They’re coming from jails, prisons. They’re coming from mental institutions. They say, ‘Please don’t say the words insane asylum.’ But I have to say it: They’re emptying out the insane asylums from all over the world. Why wouldn’t they? I would do it, if I were running Guatemala, El Salvador, Honduras, Mexico. They’re emptying out their prisons into our country.”

The Waterloo crowd cheered loudly when Trump vowed to “indemnify all police officers and law enforcement officials throughout the United States” in order to protect them when they take “strong action” in response to reports of crime.

“They’re under threat of losing their pension, their house and their family, and losing everything if they touch these people,” he said, in an apparent reference to police altercations with lawbreakers. “Our police know everything, and they can solve these crime problems very quickly — but they’re not allowed to do it… So, what I am going to do is give indemnifications to any police officer that gets in trouble for pursuing a criminal.”

Trump has expanded his lead over his rivals for the GOP nomination, and now is the first choice of 51% of likely caucusgoers, according to the latest NBC News/Des Moines Register/Mediacom poll. Trump’s lead in Iowa is the largest ever recorded at this stage of a campaign, and appears to be fueled in part by evangelical voters.

RELATED:Trump creeping closer to white supremacy advocacy