Republican presidential candidates, all of whom oppose the Iran nuclear deal, have created their own virtual worlds when it comes to dealing with the Tehran regime.

Most say that, if elected, they would cancel the agreement, get Congress to reinstate broader U.S. sanctions and then persuade the rest of the world to participate in that aggressive approach. In their telling, Iran would eventually return to the table and submit to a “better deal” than the one President Obama’s team got.

Here’s Wisconsin Gov. Scott Walker at the Aug. 6 GOP debate: “To me, you terminate the deal on day one, you reinstate the sanctions authorized by Congress, you go to Congress and put in place even more crippling sanctions in place, and then you convince our allies to do the same.”

Sen. Marco Rubio (Fla.) would be even more aggressive.

“First, I will quickly reimpose sanctions on Iran,” he said Friday in New York at the Foreign Policy Initiative. “I will give the mullahs a choice: Either you have an economy or you have a nuclear program, but you cannot have both. I will also ask Congress to pass crushing new measures that target human rights abusers and Iran’s leaders involved in financing and overseeing Iran’s sponsorship of terrorism.”

But the real world is different.

If Congress votes against the deal and overrides an Obama veto, the entire agreement collapses. In the aftermath, there is real doubt that all the countries participating in sanctions against Iran would continue, especially China and Russia. If the deal is implemented and current nuclear-related sanctions are suspended, it is even more questionable that countries would reinstate them at the request of a new Republican president if Iran is not violating the agreement.

“Foreign governments will not continue to make costly sacrifices at our demand,” was the way Treasury Secretary Jack Lew put it last week in a New York Times op-ed. Americans seem to ignore that other nations do far more trade with Iran and endure more economic pain themselves while imposing sanctions. As Lew pointed out, China, India, Japan, South Korea, Taiwan and Turkey made “costly sacrifices [to] curtail their purchases of Iran’s oil.”

Carly Fiorina, who was the star of the junior Republican debate on Aug. 6, keeps saying that her second phone call from the Oval Office “will be to the supreme leader of Iran, who may not take the phone call, but the message would be crystal clear: new deal, new deal. Until you open every military and nuclear facility to real, anytime, anywhere inspections, we will, the United States of America will make it as difficult as possible for you to move money anywhere in the global financial system. We can do that; we don’t need anybody’s help to do it.”

But the United States would need the help of others to carry out such a threat, which would require secondary sanctions against those who refuse to follow the U.S. lead. As Lew described it, “that would be a disaster,” since “the countries whose cooperation we need . . . as well as the companies and banks that handle their [Iranian] oil purchases and hold foreign reserves — are among the largest economies in the world.”

Cutting them off from the U.S. financial system, Lew said, “would set off extensive financial hemorrhaging, not just in our partner countries but in the United States as well.”

Donald Trump has perhaps gone further than other GOP candidates in creating his own set of facts to support his criticism of the Iran agreement.

“If the deal isn’t approved, they [the Iranians] still get the money” from Iran’s frozen accounts in foreign banks, Trump said more than once during a Friday CNN interview and again Sunday on NBC’s “Meet the Press.”

That is just not true.

Under the agreement, Iran’s frozen funds are released only after the International Atomic Energy Agency verifies that Tehran has implemented, probably sometime next year, various nuclear-related commitments — such as reducing to 300 kilograms the country’s stockpile of uranium enriched to 3.67 percent and cutting back the number of operating centrifuges to 5,060.

Calling it “one of the dumb deals of all time,” Trump followed up by saying on CNN: “I would have doubled the sanctions. Then I would have said before we start [negotiations], ‘I want our prisoners back.’ ”

Asked how he would have kept foreign countries as partners in doubling the sanctions before any negotiations, Trump said: “They won’t leave if I am president because they are going to respect our country and respect me. They are going to do what I want them to do. We have a lot of power over those countries.”

However, as Lew pointed out, some U.S. partners who are major importers of Iranian oil also “own 47 percent of foreign-held American treasuries [U.S. government bonds and notes]. They will not agree to indefinite economic sacrifices in the name of an illusory better deal.”

Three Republican candidates, Jeb Bush, Ohio Gov. John Kasich and Trump, have not threatened to end the agreement if they become president.

In an interview with talk-radio host Hugh Hewitt on Aug. 11, Kasich said: “Any single violation of this agreement requires the sanctions to be slapped back on with additional sanctions. And then we’ve got to see where we are.”

Trump on “Meet the Press” said, “I would police that contract so tough that they don’t have a chance.”

Bush, in an Aug. 11 foreign policy speech at the Ronald Reagan Presidential Library, said: “If the Congress does not reject this deal, then the damage must be undone by the next president. And it will be my intention to begin that process immediately.” Bush never described what a follow-up to the Iran deal would be.

He said instead, “Knowing what has gone wrong, however, is not the same as knowing how to set it right.”

On that Bush is correct.

For previous Fine Print columns, go to washingtonpost.com/fedpage.