If he cares about the benefits the special relationship brings to America, Trump should quickly visit London and apologize for his Britain First retweets last week.
Britons remain infuriated by those retweets and want their government to scale back its alliance with the Trump administration.
First, though, it's important that Trump understand why his tweets are causing such durable harm.
The principal problem is that Britain First is a far-right organization defined by thuggish intimidation. Yes, the tweets might illuminate a real problem in political Islam, but they come from a nasty messenger. Had Trump sent out the same tweets himself, he would have avoided much of the criticism he's now receiving in Britain.
But then there's the foreign policy motivation for Trump to apologize.
Consider, for example, the issue of Iran's ballistic missile aggression in the Middle East. With British support, Trump could add tighter restrictions to the Iran nuclear deal and thus constrain Iran's growing threat. But without British support, Iran will simply ignore any new U.S. sanctions and continue to benefit from its European business dealings. While Britain is leaving the European Union, its government remains the best means of persuading France and Germany to support a crackdown on Iran.
For another example, contemplate ongoing Chinese reluctance to increase sanctions on North Korea. As time runs out, the U.S. faces a choice between using force and accepting Kim Jong Un's possession of nuclear-armed missiles. But were the U.K. to tell Beijing that it is considering leaving China's Asian Infrastructure and Investment Bank, President Xi might worry about the broader economic consequences of his failure to corral Kim Jong Un. Again, the U.K. offers Trump a new means of leverage.
How about Russian aggression in Europe? Here, Trump should welcome increasing action by Britain to counter Putin's influence. He should also recognize the fact that Britain is one of just a few NATO member states that spends 2 percent of GDP on defense each year. Insulting the British government only encourages those who would rather take funny money and ignore Russian aggression.
Or maybe trade opportunities can get Trump's attention? After all, unlike many other nations, Britons buys U.S. goods and services (over $55 billion last year) more than Americans buy British goods and services. Does Trump like trade surpluses? Does he want high-value American exports and their associated jobs to grow?
Finally, there's the U.K.-U.S. intelligence relationship.
While the U.S. provides the greater share of intelligence products, Britain's foreign intelligence arms: GCHQ and the SIS are highly skilled and reliable American partners. Yet every time Trump upsets the British, he makes it more likely that they'll refuse to conduct future operations alongside the U.S.
Does this matter? Ask Mike Pompeo.
Ultimately, of course, Trump must make the right determination for his own policy priorities and for the nation. But there's a lot to lose if Trump continues to treat the special relationship like a joke. He should go to London and make a short but simple apology. Doing so, he'll shock the British people into giving him a second chance and he'll provide a close American ally, Theresa May, with a boost that might help her against a left-wing anti-American, Jeremy Corbyn.