World leaders lined up to pay tribute to Joe Biden after he announced on Sunday that he was dropping out of the US presidential race. Biden notified the public of his decision in a letter, a stunning move that upends the 2024 race for the White House. He has endorsed Vice President Kamala Harris to be the Democratic Party’s new nominee. Ukrainian leader Volodymyr Zelensky thanked Biden for taking “bold steps” in supporting his country, praising the US president’s “tough but strong decision” to end his reelection bid. “We will always be thankful for President Biden’s leadership. He supported ou…