With the skies now mostly owned by Russian fighter planes and Ukraine's military airports cratered by missile attacks, allied resupply has had to shut down the well-publicized air bridge that had shuttled planeloads of Javelins and anti-air Stinger missiles into Ukraine in recent weeks. From here on out, Ukrainian forces will have to make do with smaller convoys.

Even in the far west of the country that has been spared the worst of the fighting, these convoys are susceptible to Russian attacks. As they rumble slowly eastward to the front lines, they will have to traverse miles of potentially disputed territory.

The U.S. has been more circumspect about their commitment to provide weapons to the Ukrainians.

There is a lot of risk with the road option. NATO has ruled out the idea of setting up a no-fly zone over any part of the country, as any truck convoys driving on those roads would have little protection from the sky.

Despite repeated pleas from Ukrainian President Volodymyr Zelenskyy to close the skies, NATO, Europe, and the USA did not do so.

British Defense Secretary Ben Wallace said on Friday that NATO would have to effectively enforce a no-fly zone if British fighter jets were sent.

Pentagon press secretary John Kirby told reporters Friday that President Joe Biden has made it clear that U.S. troops will not be fighting in Ukraine.

No-fly zones are inherently dangerous, and the Obama administration refused to implement one in Syria during the height of the Assad regime's campaign against its own civilian population.

If the U.S. and its allies were to issue such an order in Ukraine, the Air Force would be forced to undertake a military mission against the invading Russian forces. Putting American planes in the sky over Ukraine would require a decision about getting in a military exchange with Russian forces.

The needs of the Ukrainian military for supplies are growing after two days of intense combat.

The life of the former adviser to Zelenskyy has been disrupted. We need everything. We need unbearable pressure on the aggressor. We need it now because bombs are landing on our children's homes.

The only viable option for the moment is the land bridge, as the western part of Ukraine, bordering NATO members Poland, Slovakia, Hungary and Romania, has been relatively quiet, and those countries could facilitate the movement of supplies.

By land or air, there is a will to keep the weapons moving so that Ukrainians can hold out for as long as possible.

Kirby said that they are going to provide additional security assistance for Ukraine. How that is going to be done is still being worked out.

Betsy Swan contributed to the report.