How Long Can Ukraine Continue Fighting Without US Support? An Analysis in the Wake of the Kellogg-Witkoff Proposal

The Kellogg-Witkoff proposal, a draft peace initiative between Ukraine and Russia promoted in particular by US Special Envoy Steve Witkoff during his visit to Moscow to meet Russian President Vladimir Putin today, appears poised to transform the geopolitical landscape surrounding the war in Ukraine. The proposal reportedly centres on a de facto ceasefire along current front lines and tacit Western acceptance of Russia’s control over Crimea and occupied parts of Donbas, in exchange for a Russian commitment to halt further offensives and allow Ukraine a path to European Union membership in the longer term. However the Ukrainian constitution forbids ceding territory without a national referendum, which cannot legally occur under martial law. If Kyiv rejects the proposal and the United States under President Donald Trump moves to strike a separate deal with Moscow—including the unilateral withdrawal of military and intelligence support from Ukraine—Ukraine and Europe will face a moment of extraordinary peril and decision-making.

Constitutional Constraints and the Dilemma of Peace

Ukrainian President Volodymyr Zelensky and the broader Ukrainian political system remain constitutionally bound to preserve national territorial integrity. Article 73 of the Ukrainian Constitution mandates that issues of altering national territory must be decided by a national referendum. Under martial law, however, no such referendum can legally be conducted, and the suspension of martial law would immediately endanger the country’s warfighting capacity and open up civil vulnerabilities.

This legal impasse makes it nearly impossible for Ukraine to accept a peace agreement that cedes Crimea, irrespective of practical realities on the ground. Thus, even if the Kellogg-Witkoff proposal were acceptable in substance to some in Ukraine’s military or political elite, it is legally and politically toxic without a decisive victory first—something increasingly elusive on the battlefield.

US Leverage and Trump’s Strategy

Should President Trump deem Ukraine’s rejection of the Kellogg-Witkoff plan as intransigence, a likely outcome could be the withdrawal of all forms of US support: military aid, precision intelligence, satellite targeting, logistical coordination, and financial assistance. This would constitute a strategic earthquake for Ukraine.

Trump’s strategic calculus might involve offering Russia a face-saving endgame, reducing European dependence on the United States, and reorienting American resources toward domestic priorities or confrontation with China. However such a strategy would come at enormous cost to Ukraine and would severely test European resolve.

Trump could seek to retain some influence over Russia through partial sanctions relief, energy diplomacy (i.e. influencing hydrocarbon prices and buying Russian oil and gas dependant upon Russian compliance), or through continuing to engage via private intermediaries, while suspending support for Ukraine. Yet without strong penalties for renewed Russian offensives, such a deal may amount to a green light for further aggression.

Can Europe Fill the Gap? Military Realities Without US Support

The immediate question becomes: Can Europe fill the loss of US support?

A. Military Aid and Munitions

Europe has already ramped up military support for Ukraine, with German, French, Polish, British and Nordic governments contributing further artillery, armoured vehicles, drones, and air defence systems. But the scale remains insufficient to fully replace American contributions:

• The US has provided roughly 60% of Ukraine’s long-range precision weapons and over 70% of real-time battlefield intelligence.

• American satellite reconnaissance and targeting data are critical for Ukrainian HIMARS strikes and drone operations.

• European production of 155mm artillery shells remains short of the 1 million annual target, though ramp-ups are in progress.

Theoretically, European states could triple their aid—but this would require massive emergency expenditures, possible rationing of military stockpiles, and an industrial mobilisation on a scale not seen since the Cold War. This could be technically achievable within 12–18 months, but it would not be immediate.

B. Troops on the Ground?

Placing European troops on Ukrainian soil—whether to man defensive lines, train Ukrainian forces in-theatre, or serve as deterrents in rear areas—remains a political taboo at the current time. Yet if Russia breaks through the front lines in the absence of U.S. support, this option may rapidly become unavoidable. The Baltic states, Poland, and France have indicated varying degrees of willingness to consider this. Germany, Italy, and the European Commission remain more hesitant.

The speed at which such a deployment could happen depends on political will and legal cover. A decision could be made in weeks; the actual deployment of brigades could take 2–3 months in a best-case scenario.

Battlefield Outlook: Summer 2025

With or without US support, the front lines in Ukraine are precariously balanced heading into summer 2025.

A. Russian Capabilities

Russia has entrenched deep defensive belts in Zaporizhzhia and Donetsk and is deploying increasingly advanced electronic warfare and drone jamming systems. With a stabilised economy, mass mobilisation infrastructure, and improved coordination, Russia could attempt significant summer offensives—especially in Kharkiv and Zaporizhzhia.

Yet Russian forces remain constrained by:

• Manpower quality: losses of experienced units remain difficult to replace.

• Supply lines: vulnerable to Ukrainian drone and long-range strike interference.

• Equipment: Though increasing in volume, much is inferior to Western systems.

Without US-assisted precision strikes, Russia might make tactical gains, but a breakthrough to strategic objectives like Kharkiv or Odesa remains doubtful unless Ukraine’s defences collapse outright.

B. Ukrainian Prospects

If US support ceases, Ukraine will face immediate constraints:

• Missile and air defence systems will rapidly dwindle.

• HIMARS and Storm Shadow strikes may become less precise without US targeting data.

• Command-and-control degradation would limit offensive coordination.

Ukraine’s ability to hold defensive lines will depend on European resupply. If Europe fails to compensate within 6–9 months, Ukrainian forces could face major attrition. The war could turn from a dynamic conflict into a grinding war of survival. However, if Europe steps in decisively—both militarily and industrially—Ukraine could hold out for years.

The Russian Economy: Can It Sustain Indefinite War?

Contrary to Western assumptions in 2022, Russia’s economy has proven unexpectedly resilient:

• Oil revenues remain robust thanks to shadow fleets and Asian buyers.

• Defence spending now makes up more than 7% of GDP, creating a war economy.

• Labour shortages are biting, but mobilisation has not yet sparked serious domestic unrest.

That said, the economy is overextended and brittle. Sustained warfare, particularly in the face of continued Western sanctions and Ukrainian strikes on infrastructure, could begin to unravel critical sectors—especially high-tech and industrial production. Russia can fight for years, but not without growing internal costs.

Consequences of US Withdrawal: Strategic Assessment

If the US exits the war and Ukraine rejects a ceasefire that cedes Crimea and parts of Donbas, the following cascade could unfold:

1. Immediate Military Impact: Ukrainian battlefield effectiveness would degrade within 3–6 months unless Europe fills the void.

2. European Strategic Crisis: The EU and NATO would face their greatest test since their founding—either back Ukraine fully or risk a wider Russian advance.

3. Potential for Escalation: Russia may interpret US disengagement as a green light for further offensives, increasing the risk of a renewed drive towards Kyiv or the northern part of the Dnipro River.

4. Political Upheaval in Ukraine: A prolonged stalemate with shrinking resources may destabilise Ukraine politically, creating openings for internal dissent or populist pressure to settle.

5. Shift in Global Order: China, Iran, and other authoritarian regimes will interpret US withdrawal as proof of American unreliability—damaging deterrence across Taiwan, the South China Sea, and beyond.

Conclusion: Months or Years?

If Europe acts decisively and cohesively—with emergency military spending, logistical coordination, and possibly boots on the ground—Ukraine can sustain the fight for years. Without such a response, and in the absence of US aid, Ukrainian military capacity could face collapse within 12–18 months. Time is of the essence.

The failure of the Kellogg-Witkoff plan, and an ensuing US disengagement, will not end the war. It will instead shift the burden squarely onto Europe’s shoulders. Whether Europe rises to this challenge will define not only Ukraine’s future—but the future of European security for a generation.