Ukraine has been fighting the war against Russia for over two years with defensive aid supplied by the U.S. and its European allies.

But as the war of attrition rages on, Russia has recently seen some small advances and Ukraine has begun to face down the possibility that more aid from Washington may not be coming. 

«It’s quite dire, it’s quite serious,» George Barros, a Russia analyst and leader of the Geospatial Intelligence Team for the Institute for the Study of War, told Fox News Digital regarding Ukraine’s defense supply shortages.  

Ukrainian soldiers of a mortar team in the 24th brigade are seen at positions near Toretsk, Ukraine, on Tuesday as the war between Russia and Ukraine continues.  (Wolfgang Schwan/Anadolu via Getty Images)

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«The Ukrainians don’t actually have what they need to wage a more successful defense,» he said. «The collective Western coalition supporting Ukraine has ensured that we’ll supply Ukraine with enough, and we’ll keep them on a starvation diet.»

«But we’ve also given them enough that they don’t have sort of a catastrophic defeat,» he added. 

The Biden administration has pledged to continue backing Kyiv, but Congress’ inability to pass substantial assistance measures means Ukrainian soldiers are bearing the brunt on the front lines.

«If they don’t get that critical resupply, then I think there’s a substantial chance that the Russians actually very well may achieve a breakthrough in 2024,» Barros said.

Kyiv and other European allies have repeatedly warned that if Russian President Vladimir Putin is able to gain a foothold in Ukraine, he is unlikely to stop there. 

Barros pointed out that while the U.S. has carried the weight in terms of the sheer amount of military aid supplied to Ukraine from a single nation, Europe has significantly increased its spending when it comes to defensive aid for Ukraine.

Ukrainian soldiers conduct combat drills in woodlands in Donetsk Oblast, Ukraine, on Saturday.  (Wolfgang Schwan/Anadolu via Getty Images)

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«The European Union and all of its constituent members, including the U.K., they are actually outspending the United States just on defense in terms of supporting Ukraine,» he said. «Unfortunately, when the Europeans break ground on a new artillery or ammunition factory, that’s not something… that comes online right away.»

«You don’t flip a switch and all of a sudden you have huge output,» he added. «It takes years.»

«But the United States, until those factories become fully operational, has to continue playing this strategic bridging role,» Barros said.

It’s not just a lack of ammunition that has slowed Ukraine’s ability to advance on Russian lines or stop it from making small gains.

Ukraine’s air defenses have become depleted.

Not only are Ukraine’s air defense missiles believed to have run critically low, and its air force degraded after years of fighting with Soviet-era warplanes, but Russia has begun carrying out attacks deep within Ukraine’s interior against critical infrastructure. 

Ukrainian soldiers of a mortar team in the 24th brigade are seen at positions near Toretsk, Ukraine, on Tuesday.  (Wolfgang Schwan/Anadolu via Getty Images)

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Barros explained that the Russian military regularly conducts highly intensive bombing campaigns against Ukrainian infrastructure like dams, power plants and bridges using cruise missiles, hypersonic missiles and ballistic missiles sourced from Iran.

Though Ukraine does have some air defense systems provided by international allies like U.S. Patriot Missile systems, it does not have enough defenses to protect its interior infrastructure as well as its front line positions. 

«The Russians have demonstrated in the last three months that they are adapting, they are implementing some lessons learned, and they are actually doing some military learning — which is improving the effectiveness and lethality of the Russian military,» Barros said.

«We think what the Russians have realized is that if they time and sequence their major strategic strikes against Ukraine’s critical infrastructure, at the same time in which they run fighter bomber aircraft to provide strike support, air support, for ground operations on the front line… they saturate the Ukrainians’ air defense bandwidth,» he added. «[Kyiv has] to pick and choose between, do they provide coverage to the frontline positions or do they protect the critical infrastructure in the major strategic cities?»

This photo taken from video released by the Russian Defense Ministry Press Service on March 13 shows the destruction of a Ukrainian Armed Forces helicopter at the jump site of an undisclosed location in the Donetsk region, eastern Ukraine. (Russian Defense Ministry Press Service via AP)

This strategy has enabled Russian pilots to run combat missions to get close to Ukraine to launch glide bombs, further obliterating Ukrainian positions.

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Barros warned that if Russia is able to gain uncontested air superiority, Moscow could begin running carpet bombing campaigns like it has in Syria. 

«Frankly, there’s no reason to doubt that the Russians would not do that,» he said. 

Ukraine has largely been able to hold its positions on the front lines for months, but military experts agree that it will not be able to do so for long. 

«Ukraine will lose this war if the United States does not continue supporting Ukraine,» Barros said.