WASHINGTON - President Donald Trump tweeted thanks to his supporters on Sunday from the hospital where he is being treated for COVID-19, after a series of contradictory messages from the White House caused widespread confusion about his health.Trump, who was taken to the Walter Reed National Military Medical Center on Friday, released a four-minute video on Saturday in which he said the "real test" of his condition will come over the next few days. "Over the next period of a few days, I guess that's the real test, so we'll be seeing what happens over those next couple of days," Trump said into the camera, looking tired and wearing a jacket and open-necked shirt.Doctors expect to provide an update on Trump's medical condition at 11:30 a.m. ET (1530 GMT), officials said.Trump's illness has upended the campaign ahead of the November presidential election and cast a spotlight on the president's handling of the pandemic. The Republican president is trailing Democratic rival Joe Biden in opinion polls.A Reuters/Ipsos poll published on Sunday found that Biden had opened a 10 point lead over Trump nationally, slightly wider than it has been for the past two months. Some 65% of Americans said Trump likely would not have been infected had he taken the virus more seriously -- a view that half of registered Republicans polled supported. Some 55% said they did not believe Trump had been telling the truth about the virus.Trump's campaign vowed that Vice President Mike Pence, who would assume the presidency if Trump were unable to carry out his duties, would have an "aggressive" campaign schedule this week, as would Trump's three oldest children."We can't stay in our basement or shut down the economy indefinitely. We have to take it head-on," Trump campaign senior adviser Jason Miller said on ABC's "This Week" on Sunday.Trump has repeatedly played down the threat of the pandemic, even as it has killed more than 208,000 Americans and hammered the US economy.In an early morning tweet on Sunday, Trump said "Thank you so much!" - referring to supporters who gathered on Saturday night outside the Walter Reed hospital waving Trump 2020 flags.CONDITION UNCLEARDiffering assessments of Trump's health from administration officials on Saturday left it unclear how ill the president had become since he tested positive for the coronavirus on Thursday night.A White House team of doctors said on Saturday morning Trump's condition was improving and that he was already talking about returning to the White House.Within minutes, White House chief of staff Mark Meadows gave reporters a less rosy assessment, saying, "The president's vitals over the last 24 hours were very concerning and the next 48 hours will be critical in terms of his care. We're still not on a clear path to a full recovery."Meadows, whose initial comments were delivered on condition that he not be identified, altered his tone hours later, telling Reuters that Trump was doing "very well" and that "doctors are very pleased with his vital signs."Meadows did not clarify the discrepancy in his comments. A Trump adviser who spoke on condition of anonymity said the president was not happy to learn of Meadows' initial remarks.Administration officials have described the move to Walter Reed as precautionary and said Trump would stay for several days.However in an interview with Fox News broadcast Saturday night, Meadows revealed that Trump's condition on Friday was far worse than officials had made public, saying doctors recommended the president go to the hospital after seeing he had a fever and his blood oxygen level dropped rapidly.White House doctor Sean P. Conley told reporters outside the hospital on Saturday that Trump had not had trouble breathing, and was not given oxygen at Walter Reed.He declined to give a timetable for Trump's possible release from the hospital, and later had to issue a statement saying he misspoke after appearing to suggest Trump had been diagnosed as early as Wednesday.In a statement on Saturday evening, Conley said the president was "not yet out of the woods" but his team remained cautiously optimistic.CAMPAIGN RESHAPEDWith Trump off the campaign trail indefinitely, his campaign announced "Operation MAGA," based on his slogan "Make America Great Again," which will see high-profile allies including Pence and Trump's elder sons, Donald Jr. and Eric, take over in-person campaigning this week.Pence, who tested negative on Friday, is scheduled to debate Democratic vice presidential nominee Kamala Harris on Wednesday.Biden, who largely avoided direct criticism of Trump during a campaign trip to Michigan on Friday, took a more aggressive tone on Saturday while speaking to a transit workers' union, even as he wished the president well."I'm in a little bit of a spot here, because I don't want to be attacking the president and the first lady now," Biden said, adding he hoped Trump and his wife Melania, who also has the illness, make a full recovery.But he quickly turned to Trump's response to the pandemic, calling it "unconscionable" and blasting Trump's comment in an interview this summer that "it is what it is" when asked about the death toll.Biden, who tested negative on Friday, told reporters he would next be tested on Sunday. His campaign will begin releasing the results of each test, a spokesman said.Conley said Trump had received the first two doses of a five-day course of Remdesivir, an intravenous antiviral drug sold by Gilead Sciences Inc that has been shown to shorten hospital stays.He is also taking an experimental treatment, Regeneron's REGN-COV2, as well as zinc, Vitamin D, famotidine, melatonin and aspirin, Conley has said.A number of other prominent Republicans have also tested positive for coronavirus since Trump's announcement, including Republican senators Mike Lee, Thom Tillis and Ron Johnson, former White House senior adviser Kellyanne Conway and former New Jersey Governor Chris Christie.