(CNN)President Donald Trump acknowledged for the first time on Sunday that Joe Biden won the presidential election, but the President refused to concede and blamed his loss on a string of conspiracy theories.

Most news networks declared Biden the victor more than a week ago. Since the call was made, Biden has given a victory speech and gotten his transition team up and running. But Trump, who had questioned the validity of the election before votes had even been cast, is continuing to dig in his heels on unsupported legal challenges lodged by his allies over vote counts in several states and asserting that the fight has only begun.

"He won because the Election was Rigged," Trump said in one Sunday morning tweet. In another, he stood by his false belief he may be able to win the election and refused to concede, writing, "I concede NOTHING! We have a long way to go."