Following his meeting with German Chancellor Angela Merkel on Monday, President Obama said that he would wait to see whether the diplomatic offensive of the German chancellor and the French president achieves any success. However, he added that, “if, in fact, diplomacy fails, what I’ve asked my team to do is to look at all options—what other means can we put in place to change Russian President Vladimir Putin’s calculus—and the possibility of lethal defensive weapons is one of those options.”

Some believe that the “hard” fall-back position sponsored by Washington can reinforce the “soft” approach preferred by the Europeans. I tend to doubt the effectiveness of the threat of military aid to Ukraine. Not to mention the risks, which are enormous.

As my colleague Jeremy Shapiro has written, I also believe U.S.-provided lethal arms may “fail to induce a Russian retreat and instead cause an escalation of the war.” The higher strategic stakes, historic and cultural ties, and geographic proximity all give Moscow an intrinsic advantage in case such escalation takes place—an actuality that my other Brookings colleagues Fiona Hill and Clifford Gaddy have described as Putin’s “escalation dominance” in Ukraine.

The emerging transatlantic differences in approaches to curb Russia’s aggression against Ukraine should not be overlooked in Washington. Nor should they be papered over, as President Obama did in his response to a journalist’s question that “there may be some areas where there are tactical disagreements; there may not be.” Russia has proven itself adept at leveraging these differences and utilizing them to its advantage.

If Russia’s actions have reinforced transatlantic unity, as Obama maintains, then European and American leaders must speak and act with coordination and coherence.

Their policies should converge in:

Conducting hard negotiations with Putin in small multilateral circles;

Modulating the pressure of economic sanctions;

Generously helping the troubled Ukrainian economy (as Daniel Wolfe and others suggest); while

Honestly declaring that Kiev’s entry in NATO is not “à l’ordre du jour.”

A corollary for my American friends, in discussing costs and burden sharing: please appreciate the fact that sanctions are already costing the European economies far more than any conceivable supply of “lethal” or “non-lethal” defensive weapons to the Ukrainian military would cost the United States and its NATO allies. It’s also worth noting the heavy toll that Europeans would be required to pay if American-supplied weapons and technology foment a full-fledged war on Europe’s doorstep.