Britain is America's closest, most historically reliable ally. And it desperately needs President Trump's help. The European Union is refusing to yield on a key Brexit issue, the so-called Irish backstop. And this is preventing Britain from getting Brexit out of Parliament.

More on that in a moment, but first, let me explain how Trump might pressure the EU. The president could address EU leaders, perhaps via Twitter, and say, "If the EU doesn't want to work with Britain on the Irish backstop, that's fine. But in that case, the EU can forget about a U.S. trade deal, forget about U.S. acquiescence on tariffs threats, forget about continued military basing in Germany, Italy, and Spain (we can move to pro-British/pro-American Poland), forget about U.S. private investment facilitation, and forget about the continued provision of boutique U.S. intelligence capabilities" (which have saved hundreds of European lives over the past five years).

So what's going on with the backstop?

Well, Prime Minister Theresa May's Brexit withdrawal agreement with the EU is struggling to win parliamentary support because the EU is refusing to give May what she needs — a contingency border arrangement between the British territory of Northern Ireland and the the Republic of Ireland, an EU member state. The backstop would enter force only if the EU and Britain fail to agree to a long-term political-economic arrangement by the end of 2020.

However, many British parliamentarians hate the backstop per se because they regard it as incompatible with British sovereignty. This blocks May's plan from parliamentary passage. And that's a problem because May's plan is the best available: balancing Britain's restored sovereignty to EU economic access. With a withdrawal deadline at the end of March, and the consequences of a no-deal Brexit potentially catastrophic in social and economic terms, the risks here are significant. The question of political morality here is important because Britain has already given up much more to the EU than the EU has given up to Britain.

But there is new hope. On Tuesday, May united a plurality of parliamentarians around renegotiating the backstop. That's where Trump should step into the breach. He should push the EU to accept either a time limit on how long the backstop would last in any scenario or to accept an arrangement that trusts cross-border traders as implicitly compliant with British-EU trade regulations.

There is little risk for either side of those proposals, but the EU says it won't go back to the negotiating table. Why? Because the EU is arrogant and wants to punish Britain for daring to leave.

I recognize that my suggested Trump threats are pretty extreme. But so is the EU's position toward America's closest ally. Trump should educate the EU to a new reality.