President Donald Trump. REUTERS/Jonathan Ernst During Friday's press conference with German Chancellor Angela Merkel, President Donald Trump repeated the big idea about trade that has been floating around his White House lately.

Trump told Merkel and the press that Germany had gotten the better end of the stick in trade deals with the US in the past and that he was looking to rectify that situation.

"The negotiators for Germany have done a far better job than the negotiators for the United States," he said. "But hopefully we can even it out."

We know what "even it out" means, and it is an absurd notion. It means negotiating a bilateral trade deal with Germany and somehow ignoring the rest of the rest of the European Union.

Of course, that can't happen. The US has to negotiate with the EU as a whole.

Merkel made sure to remind Trump of that fact — literally saying, "The European Union is negotiating those agreements for all of the member states" — after having told reporters she was "deeply convinced" that the EU is integral to the success of Germany's economy.

"The success of Germany ... has always been one in where the German success is one side of the coin, and the other side of the coin is European unity," she said.

Of course, what Merkel says about it doesn't matter in a White House that is gripped by the delusion that Germany can just tell the EU to take a hike — at least, it will be gripped by this for as long as that policy is directed by Trump's trade head, Peter Navarro.

Navarro, in a much-derided speech this month, said Germany "uses the argument" of being in the eurozone to avoid trade deals with the US, and that because of this Germany would be "one of the most difficult trade deficits we're going to have to deal with."

Navarro has gone as far as to accuse Germany of being a currency manipulator for using the euro. He thinks that because countries with weaker economies than Germany's are factored into the euro's value, Germany can sell its manufactured goods more cheaply than it could if it had its own currency.

Obviously, that's not currency manipulation. That's just the reality of the euro's makeup.

But it means Merkel faces a scenario in which the president of the United States and his top trade adviser think one of their closest and most important allies is lying to them about its need to respect the EU. Trump and Navarro think this is a choice Germany is making about the US, not an obligation that is part of the fabric of its political and economic systems.

To be fair — and this is where we see fragmenting in the White House — some members of Trump's economic team, like Commerce Secretary Wilbur Ross, have said they understand Germany isn't a currency manipulator.

But that isn't enough. The last thing we need is a White House that is irrationally angry at Germany, an important ally, because it's pushing for a trade deal that cannot realistically happen.

It's bad enough when presidents unnecessarily anger the US's enemies. We don't need one who unnecessarily aggravates its friends, too.