President Joe Biden and Ukrainian leader Volodymyr Zelenskyy signed a 10-year security agreement on Thursday. They hailed this agreement as a milestone in relations between their countries. However, Zelenskyy expressed concern about how much longer he could count on America’s support despite this agreement.

Zelenskyy also said his country “urgently” needed additional air defense systems to protect Ukrainians and the nation’s infrastructure from Russia‘s continued bombardment.

The leaders signed the agreement on the sidelines of the annual Group of Seven summit, held this year in Italy, and Biden said the goal “is to strengthen Ukraine‘s defense and deterrence capabilities.” 

Zelenskyy said at a joint news conference that the signing made for a “truly historic day,” but he also wondered about the durability of support from the United States and other allies.

Ukraine’s president said the right question to ask is “for how long the unity in the world will remain? The unity in the U.S., together with European leaders” and how it will be influenced by the outcome of elections this year in many of those countries. 

Topping that list is voting in the U.S. in November in a campaign that could see the return of Republican Donald Trump to the presidency. Trump has been skeptical of providing additional military aid to Ukraine, at one point criticizing the “endless flow of American treasure.” He more recently has expressed openness to lending money instead and has said Ukraine’s independence is important to the United States.

Zelenskyy went on to deliver a stark warning about Russian aggression, saying that “if Ukraine does not withstand, the democracy of many countries, I am sure, won’t withstand either.” 

The U.S. and European countries also agreed to keep sanctioned Russian assets locked up until Moscow pays reparations for its invasion of Ukraine, clearing the way for a $50 billion loan package for Ukraine. Combined with new sanctions against Russia announced earlier in the week, Biden said the series of actions to support Ukraine show Putin that “he cannot wait us out. He cannot divide us.”

The highly anticipated agreement will leverage interest and income from more than $260 billion in frozen Russian assets, largely held in Europe, to secure a $50 billion loan from the U.S. and additional loans from other partners. Ukraine will receive the first payments sometime this year, but it will need time to use all the money, a U.S. official said Thursday. The official spoke on the condition of anonymity to preview the agreement, which will be included in the G7 leaders’ communique on Friday

Ukraine will be able to spend the money in several areas, including for military, economic, humanitarian and reconstruction needs, the official said.

The leaders’ statement on Friday will also leave the door open to confiscating the Russian assets entirely, for which the allies have yet to secure the political will, largely citing legal and financial stability concerns.

Biden and Zelenskyy met Thursday for the second time in two weeks to discuss the security agreement as the international group of wealthy democracies has been looking for new ways to bolster Ukraine’s defenses against Russia. 

The agreement on how to use the frozen Russian assets to benefit Ukraine comes several months after the White House broke through a logjam in Congress that stalled approval of some $60 billion in U.S. aid for Ukraine. The delay gave Russia time to make up ground on the battlefield. Biden publicly apologized to Zelenskyy for the holdup when they met last week in France.

The agreement does not commit U.S. troops directly to Ukraine’s defense against Russia. That is a red line drawn by Biden, who does not want the U.S. pulled into a direct conflict with nuclear-armed Moscow.