• Biden on Sunday ended his campaign to seek reelection in November and endorsed Vice President Kamala Harris as the Democratic Party's nominee.
• The U.S. election comes at a critical juncture of a growing rivalry with China, as well as ongoing geopolitical conflicts in Gaza and Ukraine.

U.S. President Joe Biden on Sunday dropped his reelection bid and and backed Vice President Kamala Harris as the nominee of the Democratic Party, eliciting reactions from leaders worldwide.

Biden was under pressure from his party members to exit the race against former President Donald Trump, following a poorly received debate performance.

Canadian Prime Minister Justin Trudeau called Biden "a true friend" and a "partner to Canadians."

"I've known President Biden for years. He's a great man, and everything he does is guided by his love for his country. As President, he is a partner to Canadians — and a true friend. To President Biden and the First Lady: thank you," Trudeau wrote in an Instagram post.

U.K. Prime Minister Keir Starmer said he believed Biden made the decision based on what was best for the Americans, adding that he looked forward to working together for the remainder of his presidency.

Biden's "difficult" decision was acknowledged by Polish Prime Minister Donald Tusk and Czech Prime Minister Petr Fiala as driven by the larger interest of the U.S.

"Dear President @JoeBiden. You've taken many difficult decisions thanks to which Poland, America and the world are safer, and democracy stronger. I know you were driven by the same motivations when announcing your final decision. Probably the most difficult one in your life," Tusk wrote on social media platform X.

Similarly, Fiala highlighted that Biden's move was "a responsible and personally difficult step, but it is all the more valuable."

Australian Prime Minister Anthony Albanese praised Biden for acting in what the latter believed to be the best interests of the U.S., "as he has done his whole public life."

Israeli Defense Minister Yoav Gallant thanked Biden for his "unwavering support of Israel over the years."

"Your steadfast backing, especially during the war, has been invaluable. We are grateful for your leadership and friendship," Gallant wrote on X.

The Biden administration's backing of Israel in its war against Hamas in Gaza cost him a significant amount of political capital internationally, experts had observed.

Ukrainian President Volodymyr Zelenskyy also expressed gratitude to Biden's "unwavering support."

"We will always be thankful for President Biden's leadership. He supported our country during the most dramatic moment in history, assisted us in preventing Putin from occupying our country, and has continued to support us throughout this terrible war," he said.

In March, Biden asserted that Kyiv could prevail against Moscow if the U.S. continued to stand with Ukraine "and provide the weapons it needs to defend itself," but stopping short of deploying U.S. troops to Ukraine.

Kremlin spokesman Dmitry Peskov said that there were still four months until the elections, which is "a long period during which a lot can change."

Speaking to a Russian media outlet, Peskov said, "We need to be patient and carefully monitor what happens next," according to a Google translation of his statement in Russian.

"Our priority is achieving the goals of the SVO [special military operation] , not the results of the elections in the U.S.," the spokesman was quoted as saying.

Former President Barack Obama praised Biden's "outstanding track record," and called him a "dear friend and partner."

"For him to look at the political landscape and decide that he should pass the torch to a new nominee is surely one of the toughest [decisions] in his life," Obama wrote.

Correction: This story was corrected to reflect that Donald Tusk is prime minister of Poland. A previous version misstated his title.