(CNN) -- As Western leaders gather in Newport, Wales, for this week's NATO summit, the Ukrainian army is taking a pounding from Russia-supported rebel fighters in the country's east and south. The central question now confronting President Barack Obama and colleagues is whether to supply Kiev with heavy arms. So far, Obama and German Chancellor Angela Merkel, the two key decision makers, have been reluctant. But with Ukrainian forces reeling before what many are calling an overt Russian invasion, pressure is growing on them to reconsider. Already NATO has announced plans to strengthen the defense of its frontline members in the Baltics and Eastern Europe. The alliance is planning to create a rapid reaction force, made up of 4,000 troops, to respond within hours to any future Russian incursion.
@highlight
Daniel Treisman: Ukraine is much weaker than Russia, needs aid to hold its own
@highlight
He says there are powerful arguments on both sides about whether to send military aid
@highlight
Aid could lead to Russian escalation but doing nothing would condone Putin's actions, he says
@highlight
Treisman: Argument for arming Kiev is stronger than it has ever been
Equipping Kiev with greater firepower might well provoke an escalation from Russia, whose forces grossly outnumber those of @placeholder.