Donald Trump’s claim that the 2016 presidential election is “rigged” against him has become a central part of his closing argument to voters in the final days of the campaign, as the Republican nominee insists that a growing range of “corrupt” public institutions are to blame for his sharply narrowing path the White House.

As he heads into a potential loss on Nov. 8, Trump has expanded the scale and scope of his accusations to include Democratic rival Hillary Clinton, the media, establishment leaders from both parties and unidentified “global financial powers.”

“When the people who control the political power in our society can rig investigations like [Clinton’s] investigation was rigged, can rig polls, you see the phony polls, and rig the media, they can wield absolute power over your life, your economy and your country and benefit big-time by it,” Trump told a crowd this week in St. Augustine, Fla. “They control what you hear and what you don’t hear, what is covered, how it’s covered, even if it’s covered at all.”

The “power structure” he describes, according to a review of his speeches this week, includes banking institutions, the judiciary, media conglomerates, voting security experts, Democratic tricksters, scientific polling and also perhaps military leaders. He has also accused Clinton of meeting “with international banks to plot the destruction of U.S. sovereignty to enrich these global ­financial powers, her ­special-interest friends and her donors.”

By emphasizing such rhetoric, the GOP nominee — who has a history of circulating unsubstantiated accusations — has sowed distrust in basic democratic institutions among his supporters. A USA Today/Suffolk University poll released this week found that more than two-thirds of Trump supporters think the election results could be manipulated, and 43 percent say corruption will be to blame if he loses.

At a rally in Toledo, Oct. 27, Republican presidential nominee Donald Trump criticized the agenda of his Democratic opponent Hillary Clinton, saying that “her policies are so bad.” (The Washington Post)

“It’s a rigged system like Donald says, it really is,” Kelly Brooks of Mooresville, N.C., said at a Trump rally in her state this week. “I think it’s intentionally rigged, 100 percent. They don’t like Donald Trump. They don’t like change, they want to do things the way they’ve been doing them for a long time.”

Many critics are concerned by the extent to which Trump is relying on grand conspiracies to explain away his electoral troubles, including some who hear unnerving echoes of historically anti-Semitic rhetoric in Trump’s references to global elites and nefarious bankers.

Jonathan Greenblatt, director and chief executive of the Anti-Defamation League, said Trump’s references to the collusion of global banking elites sound as though they are “straight out of the Protocols of Zion,” an infamous anti-Semitic tract. Greenblatt said that he does not know whether Trump has used this language intentionally, but sees similar language and conspiracies circulated on anti-Semitic sites and blogs.

“I’m not saying that the candidate is intentionally doing this, but whether it’s the speechwriters or his supporters, we’re seeing tropes and stereotypes about Jews dominating the global banking system,” Greenblatt said. “It’s impossible for me to ascertain what’s the intent, but what I’m concerned about is the outcome. . . . We know that prejudice tends to flourish in these moments of uncertainty.”

From endorsing to un-endorsing and back again, here's a look at the Republicans who say they can no longer endorse Trump, but can still vote for him. (Jenny Starrs/The Washington Post)

Trump’s candidacy has attracted enthusiastic support from white nationalists, neo-Nazi groups and vocal conspiracy theorists such as Alex Jones, a fringe conservative radio host who has interviewed Trump on his show and who railed this week against “the Jewish mafia” who are “going to scam you.”

The Trump campaign declined to comment. The candidate has repeatedly dismissed accusations that his campaign has fostered or encouraged such messages and has said he condemns them.

Much of Trump’s conspiracy talk in recent weeks has focused on the polls, most of which show him trailing Clinton both nationally and in battleground states. Trump tells supporters that they should not believe polls that show him losing to Clinton and insists that he will win nearly every battleground state unless voter fraud is involved.

“What they do is they show these phony polls where they look at Democrats, and it’s heavily weighted with Democrats, and then they’ll put on a poll where we’re not winning, and everybody says, ‘Oh, they’re not winning,’ ” Trump said at a small produce farm in Boynton Beach, Fla., on Monday.

Trump has long made a punching bag out of the media, and a large portion of his supporters deeply distrust fact checks of his claims. He alone, he has told supporters in the final days of the election, is speaking the truth.

“The media, the special interests, Wall Street, the career politicians — the system is rigged, and I’ve been saying it for a long time,” Trump said at a campaign stop in Johnstown, Pa., last Saturday night. “And, believe me, I’m right. But with your help, we are going to beat the system and we are going to unrig the system.”

On Tuesday, Trump insisted that a hacked email revealed by WikiLeaks proved that President Obama knew about Clinton’s use of a private email server as secretary of state, despite the president saying he learned about it through media reports. While the emails showed within Clinton’s orbit about the president knowing that she used a nongovernmental email address, they do not prove that Obama knew about the server while Clinton was using it.

Trump has also repeatedly sought to undermine the Justice Department and the FBI in claiming that the investigation into Clinton’s use of a private email server during her tenure as secretary of state was unfair because it resulted in no charges against her. “This is our country, in terms of justice, has never reached a lower point than what we’re witnessing today,” he said in Tampa on Monday.

He has also claimed, without proof, that donations to the wife of a top FBI official from the political organization of Virginia Gov. Terry McAuliffe (D) shows the federal probe was favorable to Clinton.

“She never had a chance of being convicted, even though everybody in this audience, and, boy, do we have a lot of people, everybody here knows that she’s 100 percent guilty. Horrible,” Trump said in Tampa.

Trump has intensified his criticism of the media, telling his supporters that they are not just out to get him but are going after them, as well.

The angry rhetoric has sometimes prompted even angrier outbursts from his supporters. “F--- CNN!” one man shouted at a rally in Sanford on Tuesday afternoon.

“When they interview the people standing on the line, and they say, ‘Trump, Trump, Trump, Trump,’ they say, ‘All right, let’s get out of here,’ ” the GOP nominee said.

Les Adams, a Vietnam War veteran from Tallahassee who attended the Sanford rally, agreed that the media has unfairly piled on Trump in recent weeks and said that skewed sampling by pollsters is the reason Trump isn’t faring better in surveys. Adams also said he fears violence on the horizon if Clinton is elected.

“It starts with the average American saying, ‘Hell, no, I’m not going to take this anymore.’ And if Clinton gets elected? I’ll buy more guns. I’ll buy more guns. There’s going to be a revolution,” Adams said. “We can’t get much more divided without violence happening. . . . I hope it doesn’t [come to that]. I haven’t shot anybody since Vietnam; I don’t want to start now.”