It doesn't take much for somebody to seem like a more reliable party to make a deal with than Trump. Trump has already made direct threats of military action against Europe. Making a deal together with China might be the better option.
Also, Trump asking the EU and other allies to contribute seems much more to be about shifting blame and cost. Participating in the quagmire he created, with such an unreliable partner seems like a terrible idea.
Also, Trump asking the EU and other allies to contribute seems much more to be about shifting blame and cost. Participating in the quagmire he created, with such an unreliable partner seems like a terrible idea.