The administration appears to be inching closer to making a serious mistake in Ukraine:

The U.S. government is considering providing Javelin antitank missiles, small arms and ammunition to Ukrainian forces, part of an effort to try to deter further aggression by Russia-backed rebels in eastern Ukraine, according to U.S. officials.

One of the many reasons why arming Ukraine is a terrible idea is that it opens the door to demands for ever-increasing military assistance when the initial shipments fail to have the desired effect. Suppose that the administration decides to provide these weapons to Ukraine. If this fails to have the intended deterrent effect, hawks here in the U.S. will insist that the administration must “do more” as they always do. Whenever an aggressive policy fails to achieve its goal, the default hawkish answer is to be more aggressive, and that is bound to happen in this case as well. The administration might drag its feet for a while, but once it has conceded the argument to the hawks it will probably keep agreeing to new demands for larger shipments of weapons. This process will keep repeating itself again and again as the U.S. tries to prop up the much weaker side in an armed conflict in which the U.S. has almost nothing at stake.

Sending arms to Ukraine encourages both the Ukrainian government and its patrons to maintain the illusion that the conflict is going to end with something other than significant defeat for Ukraine. Marc Champion explained last week why this won’t be the case:

Yet so long as the U.S. and NATO aren’t willing to fight Russia over Ukraine (and they shouldn’t be), they should help Poroshenko understand that this conflict can end only with a settlement that involves politically painful Ukrainian concessions.

Sending arms to Ukraine tells their government exactly the opposite. It tells them that they should keep fighting on and not accept the need to make those concessions. It holds out the (presumably) false hope that more Western help can be gained in the future, which will either result in serious disappointment for Ukraine or even deeper involvement of Western governments in the conflict. Finally, it all but invites Russia to take more aggressive action to counterbalance whatever aid Western governments choose to provide.