Brussels, Belgium, hasn’t been a stage for leonine courage since King Albert I  decided to fight rather than surrender to the German onslaught of August 1914. When the United Kingdom served divorce papers on the EU last Wednesday, the reactions from the European Union’s chieftains and its members’ heads of state were a combination of fear, anxiety and rage.

EU Commission President Jean-Claude Junker, one of the first to react, seemingly blamed President Trump (who hadn’t won the Republican primary before the Brits voted for Brexit). Mr. Trump is, of course, the Great Boogeyman to the EU, because he has not only praised the Brexit vote but has predicted that other nations will follow suit.

In what Inspector Clouseau would have called “a writ of felous jage,” Junker said he’d campaign for the independence of Ohio and Austin, Texas, if the president continues to promote the idea that other nations should exit the EU.

The letter from British Prime Minister Theresa May to EU President Donald Tusk was mild, firm, and highly respectful of both the U.K. voters’ decision to leave the EU and of the EU itself. May’s letter repeated several times her desire that the terms of the U.K.’s severance from the EU and an agreement on their future relations be negotiated at the same time.

Donald Tusk meanwhile set guidelines for the negotiations that preclude the simultaneous negotiations and agreements May wants. He said the negotiations will be difficult and at times contentious. His guidelines will force that result.

Mrs. May’s letter pointed out a failure to come to a successful result on both might reduce security cooperation between the U.K. and the EU.

That drew outrage from German Chancellor Angela Merkel’s Brexit spokesman. Detler Seif told his fellow Bundestag members that Mrs. May’s statement on security cooperation amounted “… to the ultimate unprincipled blackmail attempt.”

German Defense Minister Ursula von der Leyen said, “I do not expect we are going to bargain with security topics because it’s in our common and mutual interest to exchange information.” Germany, of course, has two distinguishing features in the coming Brexit negotiations. First is the large and undiminished threat of terrorism within its borders, some of which emanates from the flood of “refugees” Mrs. Merkel welcomed in 2015. Second is the lack of German defense spending, currently set at a paltry 1.25 percent of GDP.

Ms. Von der Leyen has been rashly vocal in condemning President Trump’s call for more German defense spending, insisting at one point that Germany doesn’t owe NATO — or the U.S. — anything.

Mrs. Merkel and her defense minister are enjoying the free ride on defense we’ve given their nation since NATO was formed in 1947. Mrs. May’s words frighten them as well as the other NATO free-riders for two reasons.

First is the message brought to NATO this week by Secretary of State Rex Tillerson. T-Rex defined the president’s demands in a meeting with NATO on Friday. He told the NATO group that in their coming May summit, the president wanted them to agree not only to the minimum defense spending goal of 2 percent of GDP but also to set milestones to achieve that goal by 2024. What he didn’t define are the consequences for their failing to do so.

The Wall Street Journal reported that “German Foreign Minister Sigmar Gabriel contested Tillerson’s statement on Friday, saying it was ‘…misguided and unrealistic to think that Germany would be able to raise its defense spending by $37 billion a year to achieve the 2% level.’” That is a statement of German intent, not any reason for it.

The second reason is that two of the major EU nations — France and Germany — face national elections this year. Marine Le Pen is a candidate for the French presidency in an election that will begin later this month. Announcing her candidacy in February, Le Pen condemned the EU’s single currency and open-borders policy and promised a Brexit-like referendum on EU membership if she is elected. Last week she said the EU would die and promised to protect France from globalization.

Three weeks ahead of the first round of the French election, polls have tightened so that Le Pen and Emanuel Macron, the leftist candidate, are only one point apart. (François Fillon, the establishment candidate, is about five points behind and only four points ahead of a far-left candidate.) The possibility that Le Pen will make a strong showing in the first round has terrified the EU. The idea that she might win is unthinkable to the EU but remains a possibility.

President Obama had campaigned against Brexit. Last April, he said that if the U.K. voted to leave the EU, it would go “to the back of the queue” in trade negotiations. President Trump can, and should, push it to the front of the line.

Although the EU is the U.K.’s largest trading partner, the U.S. imported about $4.3 billion in U.K. goods in January. The U.K. imported about $3.7 billion in U.S. goods. A new trade deal between the two nations could accelerate and enlarge trade significantly.

The U.K. is one of the five NATO members (of 28) that meet the 2 percent of GDP defense spending goal. Aside from the U.S., the others are Poland, Greece, and Estonia. Each of them needs to be rewarded and encouraged to keep up its defense spending. Mr. Trump should announce trade negotiations with the U.K. and the other three and urge his negotiators to work first on a new deal with the U.K. to take effect upon its exit from the EU.

Greece is, of course, the basket case of the EU. Its continuing near-bankruptcy can’t and shouldn’t be resolved by burdening our economy or our budget, but there may be room for more trade.

We need to help those nations that are willing to invest in their own defense so that we can help them defend themselves. Their defense spending needs to be more than just pouring money on their depleted armed forces. Their spending needs to be entirely focused on operational capabilities that are designed to work with ours, just as the NATO treaty envisions.

If the president announced the opening of those trade talks, the message to Germany, France, and the rest of the NATO free-riders would be unmistakable. It would capitalize on the part of Mrs. May’s letter that suggested reduced security cooperation if the Brexit negotiations fail.

At this point, we shouldn’t abandon NATO. But hammering home the point Tillerson made about defense spending by undertaking trade negotiations with the NATO members who are living up to their obligations is precisely the right thing to do and to do right now.