World leaders are heading to Washington, D.C., this week for a historic NATO summit as uncertainty rises over continued U.S. support for Ukraine.

The summit marks the 75th anniversary since the alliance’s founding and comes as skepticism grows regarding President Biden’s chances for re-election and what that could mean as Ukraine’s war with Russia rages on. 

Several key issues are expected to be addressed at the summit that kicks off Tuesday, including Ukraine’s success in its war with Russia, Ukraine’s future within NATO and how the alliance plans to bolster its collective defense. 

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U.S. President Joe Biden and his NATO counterparts are meeting in Washington this week to mark the 75th anniversary of the world's biggest security organization just as Russia presses its advantage on the battlefield in Ukraine.  (AP Photo/Pavel Golovkin, File)

The U.S. has been a major supporter of Ukraine since the war kicked off, providing the most significant amount of aid from any one nation and sparking debate within the U.S. over whether Washington can or will keep up this level of support under a different presidency. 

Former President Donald Trump refused to clarify what U.S. involvement with NATO would look like if he were to win a second presidency, and during a debate with Biden last month he shrugged when asked, "You’re going to stay in NATO or you’re going to pull out of NATO?" 

Experts agree Trump is unlikely to pull out of NATO altogether, though the alliance is taking steps to safeguard its support for Ukraine should Washington begin to take a back seat. 

Reports surfaced last week suggesting that NATO was already pledging its support for next year by committing another $43 billion in funding for the war-torn nation in 2025. 

"I don't think NATO would explicitly say they're doing anything because of the politics of a specific member state," retired Rear Adm. Mark Montgomery, a senior fellow at The Foundation for Defense of Democracies told Fox News Digital. "But I think they do understand that Donald Trump has asked for a higher level of European state leadership within NATO, and contributions within NATO. 

"And I think they are seeing what's happening, [and] they are starting to maneuver themselves accordingly," he added. 

President Joe Biden (R) and Republican presidential candidate, former U.S. President Donald Trump participate in the CNN Presidential Debate at the CNN Studios on June 27, 2024 in Atlanta, Georgia. (Andrew Harnik/Getty Images)

Montgomery also said he expects there to be discussions surrounding the Ukraine Defense Contact Group — a coalition of more than 50 nations, including all 32 NATO nations, in support of Kyiv but which is largely headed by the U.S. under Secretary of Defense Lloyd Austin.

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"This is about the day-to-day management of the Ukraine support packages," Montgomery said, pointing out that if Trump does win the presidency, as with any administration change, it will take time to get new officials in place.  

Funding Ukraine’s defensive efforts to oust Russia over the last three years has been a costly endeavor and has sparked push back from not only Republicans in Congress but also isolationist movements in Europe as conservative lawmakers take up more seats in the European Union. 

In April, Congress approved a $60 billion aid package to Kyiv. But the months-long blockade on the package proved to be a serious setback for Ukraine, and its arms became critically depleted — revealing just how vital U.S. arms are in the war against Russia. 

It is unclear if any individual NATO nations are expected to pledge additional aid packages this week, but experts have long warned that Russian President Vladimir Putin will not be deterred in his war effort if Ukraine is not adequately supported.

"It needs to be such a significant sum of money that it's made crystal clear to Putin that he can't run the clock here," former NATO Assistant Secretary General for Defense Investment, Marshall Billingslea, told Fox News Digital. "Equally important, is that the allies need to furnish the kinds of sophisticated weapons that the Ukrainians need, and they need to do so without the ridiculous limitations that have so far been put on some of them — like the Biden administration's refusal to allow Ukraine to use U.S. weapons against Russians on Russian soil."

Ukrainian servicemen rest at their positions after a fight, as Russia's attack on Ukraine continues, near the front line city of Bakhmut, in Donetsk region, Ukraine, May 11, 2023.  (Radio Free Europe/Radio Liberty/Serhii Nuzhnenko via REUTERS)

Ukrainian President Zelenskyy has repeatedly urged the U.S. to allow him to use long-range weaponry like American-made ATACMS — precision-guided ballistic missiles — to strike military targets in Russia.

While nations like the U.K. and France do not have limitations on the weapons they provide Ukraine, the Biden administration has made some strike stipulations against hitting targets outside Ukraine — a condition NATO Secretary General Jens Stoltenberg has urged all NATO nations to abandon. 

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The alliance is expected to release additional "language" on providing a path forward for Ukraine to join NATO, though it is still highly unlikely that Kyiv will be able to pursue membership until its conflict with Russia is over.   

Billingslea explained that NATO will be looking to toe the line when it comes to Kyiv’s future in the alliance by signaling "to Putin that Ukrainian membership in NATO is in no doubt or will not be indefinitely delayed if he chooses to continue to engage in hostilities."

But the success of Ukraine and its continued international support will not be the only major topics covered. The alliance will also be looking to bolster its collective defense by addressing all international threats it faces. 

Ukrainian soldiers fire a cannon near Bakhmut, an eastern city where fierce battles against Russian forces have been taking place, in the Donetsk region, Ukraine, May 15, 2023. (AP Photo/Libkos)

"There's a coalition of authoritarians that NATO has to deal with, and that is China, Russia, North Korea and Iran," Montgomery said.

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China, Iran and North Korea have not only all backed Russia in its war in Ukraine, but they have made clear their unity is based around countering Western domination rather than simply Russia’s war aims in the former Soviet nation. 

"Ukraine is on the frontline of fighting all four of these authoritarian regimes. NATO better step up to support it," Montgomery warned.