Former US President Barack Obama broke his silence on Tuesday and handed a much-needed endorsement to Joe Biden, the Democratic presumptive nominee and his vice president for eight years. In a video released on Tuesday morning, Mr Obama, the most popular figure in the Democratic party, threw his weight behind Mr Biden. "I'm proud to endorse my friend Joe Biden for President of the United States. Let's go", Mr Obama said in a tweet on Tuesday. The former President has shied away from commenting on his party’s nomination but has played a background role in unifying the ranks around Mr Biden after he became the frontrunner in mid-February. Mr Obama has maintained contact with most of the candidates, including Bernie Sanders who dropped out and endorsed Joe Biden on Monday. The endorsement comes at a critical time for Mr Biden as his campaign gathers momentum. The former vice president won Wisconsin on Monday night and is now less than 700 delegates from clinching the nomination. It also promises an active role for Mr Obama on the campaign trail after the pandemic restrictions are over. Mr Biden has consistently emphasised his ties to Mr Obama throughout the campaign, even as the former President avoiding wading into Presidential politics since leaving office in 2016. But his status as the most popular among Democrats in the United States (YouGov poll) and the most popular of former Presidents (Gallup poll), makes his endorsement all the more valuable. Mr Obama’s backing could open the door for other high-ranking Democrats to endorse Mr Biden, such as former secretary of state Hillary Clinton, former Presidents Bill Clinton and Jimmy Carter, and former first lady Michelle Obama. It adds to the Democrats’ momentum after scoring a dramatic win in Wisconsin’s top court election on Monday. Their candidate Judge Jill Karofsky ousted Republican Justice Daniel Kelly from his seat, in only the second time a Supreme Court incumbent has been defeated since 1967. Ms Karofsky celebrated with her supporters while social distancing. But the win bodes well for Democrats’ turnout in a state that they lost in 2016. The impact of the pandemic and accusations for President Donald Trump of acting late is also shoring up support for the opposition. Mr Biden gets higher marks on handling the pandemic and according to an Economist/YouGov poll, the majority of Americans (57 percent) believe Mr Trump acted late and waited too long to take action against the spread. Cases in the US passed 588,000 on Tuesday and more than 23,000 have died from the disease in the country. Mr Trump’s approval has slipped to an average of 44 percent. Economic developments are also troubling for Mr Trump, with more than 6.6 million people filing jobless claims last week. The US President is taking fire from his own party after claiming he has “total authority” to reopen the country on Monday. Republican Congresswoman Liz Cheney rebutted that claim on Twitter. “The federal government does not have absolute power,” she said, quoting the US constitution, which states that “the powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.” But with the election more than six months away, the momentum could shift in the Presidential race following the summer conventions, if they continue to be held in mid and late August.