It's probably fair to assume that Kristen Silverberg, President George W. Bush's ambassador to the European Union, and Anthony Gardner, who served in the same capacity under President Barack Obama, disagree on many of the issues that traditionally tend to divide Republicans and Democrats in the United States. But what the two share is the conviction that the Trump administration's decision to impose tariffs on steel and aluminum from the EU is deeply misguided.

"I think it's very foolish," said Gardner, the US ambassador to the EU from 2014 to 2017. "Guns should be pointed at enemies, not at allies."

"I think it is very damaging and unfortunate," said Silverberg, who held the post from 2008 to 2009.

Undervaluing allies

Both former US diplomats had to deal with key points of friction between Washington and Brussels ― Silverberg over the Iraq War, the Kyoto climate protocol and the International Criminal Court, Gardner over the Snowden spying revelations ― but the current trans-Atlantic rift potentially runs even deeper, they said.

"It's hard to think of something quite like this," said Gardner, who before becoming Obama's top diplomat in Europe had been in charge of European affairs for President Bill Clinton's National Security Council.

"I do worry that the Trump administration underestimates the importance of the relationship to the US in the long term," said Silverberg, who served in various key roles during Bush's eight years in office prior to her posting in Brussels. "I think they fundamentally underestimate the value of allies."

Read more: US import tariffs — nerves of steel, round two

Both former officials expressed disbelief with the rationale given by the Trump administration for the tariffs against the EU: to protect US national security interests. Indeed, most EU member states, alongside the US, are also NATO members.

"It's plainly absurd," said Gardner about the Trump's administration's justification. He noted that invoking an arcane national security provision against Washington's allies in the EU to try and address President Donald Trump's real issue with Brussels, namely its trade surplus with the bloc, was not just unwarranted, but problematic because it could set a dangerous precedent.

Serious attack on global trade rules

Gardner said little is now preventing China or any other country from blocking imports on anything, unrelated to true concerns about national security. "It is a serious attack on the world's trading rules because this is clearly something that nobody wants to litigate at the WTO," he said.

Read more: Flood of sanctions worldwide increases uncertainty for small businesses

That's because, Gardner explained, even if one could win such a case of unfounded national security claims at the WTO, it would likely only feed already existing popular sentiment against unelected international judges supposedly determining other countries' national security interests.

Silverberg called the Trump administration's invoking of national security grounds as justification for what are clearly economic issues a "dangerous expansion" of the traditional interpretation of national security that could invite other nations to do the same.  

"I think this administration fundamentally misunderstands the causes of the trade deficit with the EU," she said. "They seem to be convinced that this has to do with bad trade policy, that their predecessors have struck bad deals."

'Don't confuse Americans with this president'

Despite their bleak assessment of the Trump administration's grasp of trade issues and the importance of allies, Washington's former top envoys to the EU don't think the trans-Atlantic relationship is doomed just yet.     

"I would say to Europeans and Germans: Don't confuse Americans with this president," said Gardner. "They are two different things."

While he acknowledged that Trump had significant domestic support, Gardner predicted that there would be a "reversion back to the mean and back to sensible policies." He also expressed the belief that "we can fix most of the damage."

Read more: Pompeo unveils US Iran plan: Economic strife, break with EU

Asked how Europe should deal with the Trump administration's tariff move, Gardner offered this: "I would also say to Europe: Stay united. Do not let yourselves be picked off one by one on side deals. Some countries may think they can get side deals by going to Washington and ingratiating themselves. It doesn't work."

Trump's trade deficit obsession

Silverberg said that despite the current problems between the EU and the US, the underlying foundations of the trans-Atlantic relationship ― economic, political and cultural ― still remain intact and favor close cooperation on many issues across the pond.

But, she cautioned, the EU should brace itself, because it could take some time before things get better. "This is a president who is obsessed with trade deficits and who thinks that these tariffs would be useful in bringing trading partners to the table," Silverberg said. "As long as that's the obsession, it's going to be really hard for the administration to focus on concrete issues in the trans-Atlantic relationship."