Trump has declined to certify that Iran is in compliance with the 2015 nuclear deal, despite evidence that it is.

His action is likely to further erode international confidence in the US as a partner.

New sanctions Trump announced Friday could also increase the chances of conflict in the Middle East.

President Donald Trump's campaign against the Iran nuclear deal came to a head on Friday, when he refused to certify that Iran was in compliance with the agreement.

"We cannot and will not make this certification," Trump said from the White House, calling it "one of the worst and most one-sided deals" the US has ever made and announcing new sanctions on Iran.

Trump stopped short of withdrawing from the deal or of reimposing sanctions on Iran himself, instead sending the deal back to Congress, which will have 60 days to decide whether to reimplement sanctions or alter legislation that covers US participation in the accord.

While what action, if any, the US ultimately takes remains unknown, the president's fusillades against the agreement may have already had an effect on how the rest of the world views the US under Trump.

The pact was signed in 2015 by Iran and the US, Russia, France, Germany, China, and the UK. Four of those signatories said last month that unilateral US action would be a mistake and harm US and European interests.

German Foreign Minister Sigmar Gabriel put the consequences in stark terms on Thursday, saying that Trump's drive to decertify the deal was putting a wedge between the US and Europe and pushing countries in the EU closer to China and Russia.

Trump with German Chancellor Angela Merkel. Getty Images/Pool

"It's imperative that Europe sticks together on this issue," Gabriel told the RND German newspaper group. "We also have to tell the Americans that their behavior on the Iran issue will drive us Europeans into a common position with Russia and China against the USA."

Gabriel, who is expected to leave office in the coming months, said Russia in particular was paying attention to divisions between the US and Europe — divisions that don't "exactly strengthen our position in Europe," he noted. (Foreign-policy experts in Germany have recently warned about rising anti-American sentiment there.)

"Trump's efforts to sabotage the Iran deal [are] the latest in a series of ill-considered actions that have led longtime US allies to pay less attention to Washington and to pursue a more independent course toward other major powers," Stephen Walt, professor of international affairs at the Harvard Kennedy School, told Business Insider.

Former US Secretary of State John Kerry, left, meets with Iranian Foreign Minister Mohammad Javad Zarif in 2016. Frank Franklin II/AP

"To be blunt," Walt added, "Trump's erratic behavior at home and abroad has gravely damaged confidence in US steadiness and leadership, and his policies are leaving other states with little choice but to explore other arrangements."

Gabriel's comments may simply be another episode of diplomatic and political posturing about the deal.

As Congress' final decision remains to be seen, and since other parties say they'll maintain the agreement, decertification is not a "one shot" deal, said Daniel Nexon, a professor at the Georgetown School of Foreign Service.

But, Nexon told Business Insider, "any attempt by the US to alter the framework — let alone abandon — risks creating major fractions with Germany, France, and other key allies. Doing so also creates another arena of political and diplomatic conflict with China and Russia."

Opinions on the deal within Congress are varied.

On the same day this month that Democratic Sen. Chris Murphy said the deal was the biggest obstacle to Iran acquiring nuclear weapons, Republican Sen. Tom Cotton gave a speech in which he called it the "dumbest and most dangerous" deal in US history and said it had set Tehran on the path to nuclear weapons.

Some lawmakers want to rework the terms of the agreement. Cotton, along with Republican Sen. Bob Corker, have introduced legislation that would "effectively" keep it in force longer and automatically reinstate sanctions if Iran comes within a year of nuclear capability. Such action has been criticized as unilateral and in "bad faith."

A number of Republicans in Congress, who uniformly opposed the deal in 2015, are now hesitant to undo it, fearing damage to US credibility. They instead seek other ways to restrain Iran, which has said there "will be no renegotiation." (Some Obama administration officials have criticized the idea a "better deal" even exists.)

Trump's Friday announcement also detailed additional non-nuclear-related sanctions against the Iranian government to block financing of terrorist activity and address missile proliferation.

Trump also announced sanctions on Iran's Revolutionary Guard Corps, which he called the "Iranian supreme leader's personal terror force and militia." The sanctions were implemented by the Treasury Department, and the State Department has not designated the IRGC as a terrorist organization.

A woman celebrates the tentative Iran nuclear deal. AFP / Getty Images

While decertification is not a death blow to the deal, "designating the IRGC as a terrorist organization ... would have immediate and potentially disastrous effects that could reverberate across the Middle East," Hooman Majd, an adviser to two Iranian presidents, wrote for Foreign Policy this week.

The Iranian public generally perceives the IRGC in a positive light, Majd writes, and the US calling it a terrorist force "might very well be seen by some Iranians as stopping just shy of a declaration of war against their country."

In response, the IRGC may adopt a more aggressive posture in the region, especially in the Persian Gulf, where US and Iran vessels have come into close contact. Deleterious economic effects from such a designation may also wound reformist political elements within Iran's government.

More broadly, undercutting the Iran deal is likely to further inculcate the feeling that the US is not a reliable interlocutor on the world stage.

"If you put this in the context of deciding to withdraw from the Paris Agreement, repeatedly questioning US security commitments, and the ongoing signals that Trump intends to scrap existing trade agreements, it should become clear why this move is part of an overall pattern of undermining confidence in American leadership and Washington’s ability to keep its word in international politics," Nexon told Business Insider.

An untrustworthy US is also less likely to be able to secure a deal to ratchet down tensions with North Korea.

There is little precedent for Trump's action, Nexon said. He noted President George W. Bush's 2001 withdrawal from the Antiballistic Missile Treaty signed with the Soviet Union in 1972 but pointed out that the international situation at the time somewhat insulated the US from rebuke over the move.

"This has not been the case with the targets of the Trump administration's diplomatic wrecking ball," Nexon added. "While accusations that Iran is engaged in all sorts of adversarial behavior are correct, they are clearly abiding by the agreement. This is really rogue-state territory for the United States."