Gianni Pittella argued for “blocking the appointment of [Ted] Malloch” | Frederick Florin/AFP via Getty Images Brussels threatens to block Trump’s EU ambassador If the US president picks Ted Malloch as his man in Brussels, Europe could say No.

Donald Trump's reported favorite for EU ambassador is already facing headwind in Brussels, with some officials keen to teach the American president a lesson over a potential diplomat they say is anything but diplomatic.

Ted Malloch, an economist with ties to the president’s inner circle, has raised eyebrows by comparing the EU to the Soviet Union (which he claims to have helped bring down,) saying that the bloc needs “taming.” He has also spoken disparagingly of Jean-Claude Juncker, suggesting the European Commission president "was a very adequate mayor, I think, of some city in Luxembourg and maybe he should go back and do that again."

On Thursday, the liberal leader in the European Parliament, Guy Verhofstadt, and the leader of the European People's Party, Manfred Weber, sent a letter to Juncker and European Council President Donald Tusk saying that Malloch should not be granted credentials, citing his "outrageous malevolence against the values that define this European Union."

"We are strongly convinced that people seeing as their mission to disrupt or dissolve the European Union should not be accredited as official representatives to the EU," the letter said.

Gianni Pittella, president of the Socialists and Democrats group in the European Parliament, argued in a plenary speech Wednesday for “blocking the appointment of Malloch” for his “delirious” statements. He later told POLITICO that Malloch is “not welcome here” and called on the EU to “send him back home.”

"In general, you send an ambassador to build constructive relationships — not saying you should be tamed" — Senior EU official

Privately, EU diplomats agree that Malloch would not be a suitable choice for the job.

"We still do not know what to do with the new U.S. administration," said one top EU official. "In general, you send an ambassador to build constructive relationships — not saying you should be tamed."

While it would be highly unusual for the EU to try to block an appointee, it is not impossible, though it wouldn't be up to MEPs as it is the European Commission and Tusk that issue credentials to an ambassador.

Protocol and process

Anthony Gardner, the outgoing U.S. ambassador, left his post in Brussels on January 20, going out in a blaze with a warning to Trump not to botch the transatlantic alliance.

Adam Shub, the deputy head of the U.S. mission to the EU, has served as the acting ambassador since. If everything goes smoothly, the new U.S. ambassador is likely to be in Brussels at the earliest in June.

But it could take longer.

Malloch has not yet been picked officially and any candidate will have to be vetted in the U.S. first — a process that includes FBI background checks and scrutiny of financial interests and former public statements before the candidate goes before the U.S. Senate for a confirmation hearing.

Then, to get the ambassador appointed to the EU, Washington has to send the person's resumé to the European Commission's protocol service which makes an assessment in consultation with the office of EU foreign policy chief Federica Mogherini — a procedure that usually takes about eight weeks.

EU capitals then have a month to oppose the request and unanimous consent is required for the credentials to be issued. Usually, any concerns are dealt with privately before the person has been officially announced and there is no record of the EU ever denying a request.

"I would not be surprised if some member states are going to oppose him," said Jean De Ruyt, a former Belgian ambassador to the EU, who argued that, rather than go through the process of publicly refusing him after the fact, it would be better for the Commission to hint to Washington early on that Malloch is an unacceptable choice.

One official said it would be unique for an ambassador to be refused on account of something that the person had said.

For any country or state, "it is very rare to refuse credentials" for diplomats, the official said. "Usually, they are only refused for convicted felons."

In 2015, the Vatican refused to accept the credentials of a French diplomat, Laurent Stefanini, who is gay. After a nine-month stand-off with the Holy See, Paris gave up.

"If Donald Trump nominates someone who said publicly he wanted to destroy the European Union ... it does not portend the best relationship" — Tereza Novotna, EU foreign policy expert at ULB

Without credentials, the ambassador will be an ambassador in name only and have no privileged access to top EU officials, meetings or institutions and no diplomatic privileges such as tax exemptions.

If the EU refuses to grant credentials to a candidate, another name can be put forward or the post can be left vacant, with a more junior diplomat in charge of the embassy.

For now, though, the Trump administration hasn't made an official pick or made a request for credentials.

"So let's take a step at a time," said one EU official.

But Tereza Novotna, an EU foreign policy expert and a researcher at the Université Libre de Bruxelles, said early resistance may be better.

"EU countries may need to weigh the pros and cons of the right time to protest," she said. "If you don't start at the beginning [of the process] then it will be harder to reject anyone later," she said, adding: "If Donald Trump nominates someone who said publicly he wanted to destroy the European Union ... it does not portend the best relationship."

Maïa de La Baume and Tara Palmeri contributed to this story.