The high dollar amount requested also sends a signal to Russia that the United States intends to back Ukraine in the fight for the long run. It will also likely boost Ukrainians who say they want to defeat Russia, not merely settle for a long-term stalemate.

In a White House address announcing the funding request, President Joe Biden said it is “critical this funding gets approved and approved as quickly as possible.”

He also framed the sum as a way to begin a transition from just-in-time military and economic aid to a new, long-term effort to sustain both Ukrainian civil society and backstop the young democracy. The new funding will begin “the transition to longer-term security assistance that’s going to help Ukraine continue to defend against Russian aggression,” Biden said.

The president also couched the effort in terms of a longer struggle against Russian aggression and supporting partner states in Europe. “The cost of this fight is not cheap,” Biden said. “But caving to aggression is going to be more costly if we allow it to happen. We either back [the] Ukrainian people as they defend their country, or we stand by as the Russians continue their atrocities and aggression in Ukraine.”

The $20 billion in military aid includes $5 billion in additional authority to transfer weapons and equipment to Ukraine from U.S. inventories, $6 billion for the Ukraine security assistance initiative and $4 billion for the State Department’s Foreign Military Financing program.

Biden and other top officials have warned that the previous authority to provide U.S. weapons is nearly exhausted after lawmakers permitted $3 billion in shipments of equipment last month. Most weapons shipped to Ukraine since the start of the war have been provided through the process, including transfers of Javelin anti-armor and Stinger anti-aircraft missiles drawn from military stockpiles.

The Pentagon’s Ukraine Security Assistance Initiative has hovered around $300 million annually for the past several years. So the boost to $6 billion is an increase that would put it on par with other funding lines to maintain U.S. presence and allied support in the Pacific and across Europe, clearly outlining how central the White House sees the fight in Ukraine to regional, and global, security.

“The president’s funding request is what we believe is needed to enable Ukraine’s success over the next five months of this war,” an administration official told reporters on a call Wednesday. “And we have every expectation that our partners and allies … will continue to provide comparable levels of assistance going forward.”

The latest request comes after Congress approved nearly $14 billion in emergency funding to help Ukraine last month, including billions to fund deployments of thousands more U.S. troops in Europe and to replenish depleted U.S. stocks of weapons shipped to Kyiv.

Biden’s request is likely to have near-unanimous support among members of both parties, but it’s far from certain that both chambers will be able to send it to the president’s desk quickly. Democratic leaders intend to pair it with the president’s separate request for new Covid relief funding — a move that Republicans have said would doom both packages. Despite the GOP warnings, Biden in his letter to Congress on Thursday specifically asked lawmakers to pair the two funding requests.

A document on the supplemental released Thursday morning contained few hard details, but it did list “artillery, armored vehicles, anti-armor and anti-air capabilities” as top priorities, along with “accelerated cyber capabilities and advanced air defense systems.” It also suggested that the U.S. is willing to bankroll the rebuilding of Ukraine’s industrial base, calling for money to fund “improved production capabilities for munitions and strategic minerals, and increased intelligence support.”

The administration’s proposal would earmark $16.4 billion for the Defense Department. That includes the $6 billion for the Pentagon’s account to arm Ukraine’s military as well as $2.6 billion to fund troop deployments to Europe.

The package also proposes $5.4 billion to replenish military inventories of weapons and equipment sent to front lines.

Congress already allocated $3.5 billion for weapons replenishment in the last funding package, but concerns have percolated over how long the Pentagon can sustain its transfer of weapons and how quickly industry can ramp up production to replace them — especially Javelins and Stingers.

Andrew Desiderio, Quint Forgey and Nahal Toosi contributed to this report.