We have grown used to his sharp tone, and now United States Ambassador to Germany Richard Grenell wants his voice to be heard yet again: Echoing his boss, President Donald Trump, Grenell said last week he is not satisfied with the German federal government's new budget.

He has a point: At the 2014 NATO summit in Wales, member states agreed to increase annual defense spending to 2 percent of gross domestic product by 2024. Only Germany has refused to play along.

One thing is clear: The US, NATO's single biggest contributor, is looking to reduce future expenditures by getting countries like Germany to pay more. Some countries, such as Poland, have acceded to Trump's wishes. Other countries are having a harder time doing so. Germany has reservations for historic reasons, as well as a general concern from its European neighbors. The theory goes that if Germany spent 2 percent of GDP on its military, it would outstrip all other European Union member states by far.

Attempted blackmail from the US Embassy

It is clear that Ambassador Grenell is once again meddling in Germany's domestic politics in a way rarely seen in diplomatic circles.

Shortly after taking up his post, he demanded German companies stop doing business with Iran. He said that would go against Trump's decision to withdraw the US from the Iran nuclear deal and his new sanctions against Tehran. Grenell didn't care what Germany's opinion was on those policies.

He recently threatened companies involved in the construction of the Nord Stream 2 gas pipeline, going so far as to threaten sanctions. Germany, he said, should buy US liquefied gas — it would be good for business. That is true, just not for Germany.

Read more: What's behind America's Nord Stream objections?

The German government itself has also had to put up with Grenell's threats: If the Chinese telecommunications company Huawei were allowed to build Germany's new 5G network, he warned the US might limit intelligence sharing.

Berlin would clearly lose face if it were to give in to threats of blackmail delivered from the lips of a sitting US ambassador. Indeed, thus far all of Grenell's attempts to that end have failed. It is also no secret that he has irritated the government leadership in Berlin and has as a result isolated himself in the capital. His German diplomatic counterparts even prefer to keep their distance.

Trump's lone warrior against the establishment

Germany's business-friendly Free Democratic Party (FDP), now in the parliamentary opposition, felt so provoked by Grenell that its leaders called for him to be expelled from the country last week. Deputy FDP Chairman Wolfgang Kubicki said that Grenell was acting more like "a high commissioner of an occupying power than a US diplomat."

Yet that would be exactly the kind of escalation that Trump's provocateur would love: A media-savvy expulsion that would make international headlines. It would cement his reputation as Trump's lone warrior against the establishment, his underdog in the fight against the big guys.

Nevertheless, Grenell's attempts to play the mini-Trump are not working. But how would they exactly? Grenell was not a diplomat before arriving in Germany and he likely won't be after he leaves.

And that is exactly why he should be treated like a provocateur — and why the German government shouldn't be provoked by him. Perhaps dealing with the US ambassador could provide a blueprint for dealing with his boss in Washington: Just ignore him, even if that is admittedly hard to do sometimes.