Polish Prime Minister Donald Tusk questioned US “loyalty” to its NATO allies and suggested that the EU step up its own mutual defense commitment, the latest sign of worsening transatlantic ties.

The EU has a mutual-defense clause comparable to NATO’s Article 5, but it has less weight because it lacks Washington’s backstop.

US President Donald Trump’s repeated suggestions that Washington may not honor the NATO agreement, and reports that the US is exploring removing Spain from the alliance over its failure to support the Iran war, however, have raised the EU defense agreement’s importance. European military spending is up, and France has promised to include Europe under its nuclear umbrella, including potentially basing nuclear bombers in allied countries.